Heya!
Masters Terran here, lunatic that plays bio, and solidly has TvZ as his best matchup, here to help.
Alright so I’m just going to give you a few general tips I can think of, off the top of my head.
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When asking for help, always think critically.
–> What this means is that whenever someone says something, ask why they are saying that, what is the purpose of this? Why do I build a bunker at X time and at location Y? This also really helps when looking at replays which is a 100% must. Looking at replays you gain game-sense because you understand what the opponent may or may not have, how they play and you can begin thinking what works and why. For instance, if you lose to a banebust, you can look at the replay and see if they macroed out or not, and when the game was lost.
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When asking for help on the forums, ALWAYS, and I mean ALWAYS post replays. Sc2replays works well enough, and is free and I think you can directly upload replays from sc2 although I’ll probably be corrected by some forum ninja, that claims Twitch Gm. Anyhow, they’ll provide huge insight into how you play for someone like me, I’ll see, Oh. You overmicroed here, you forgot to make production, too few workers, unoptimal build locations, poor multitasking ect… Then, I can begin to construct why you should / should not do something, and that is hugely beneficial to both of us (You’d be surprised how much you can learn from lower level players, we’re not good until like GM 
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Here’s some solid advice. Take basically anything from sc2 forums with a heap of salt, unless they give huge analysis and are pretty nice, and or open minded. Chances are, people are opinionated and biased. In my limited experience of forum browsing, I’ve seen plenty of trolls and other kinds of people claiming to know what is right and what is wrong, but fail to hold up, under any amount of scrutiny.
TRIGGER WARNING
- Never. Ever. Blame. Balance. You. Complete. Banana.
As a mid masters, who occasionally takes a game or two off of GM’s I’m not even eligble to say what is balanced or not, because ultimately, I suck at the game. like 99% of the time, when I lose it’s because I messed up a positioning, took a bad fight, was floating resources for several minutes (mainly because I personally have a vandeta against supply depos, just check my average time supply blocked >.< 2 minutes or so )
Balance is not the cause of your loss, in any regard. Especially in the lower leagues, you can make so many mistakes. I’ve yet to see a game that I’ve genuinely lost because of balance, and not some mistake I’ve made. That’s how this game works. Now, I’ve been from bronze to masters climbing all the ranks, over the last few years. So, I’d recon my experience somewhat valid but I’m probably mistaken. Anyhow I digress.
Just see what you could have done, you won’t impact balance regardless. Find a way to combat whatever you have done and trust me, sooner or later you’ll whoop your opponents posterior (A ss aint allowed for some reason). 
- I’m going to give you TvZ specific tips now.
If you’re running 2-1-1, 16 marine stim timing, You do not under any circumstance trade your drop. I’m the lunatic that still uses it to kill GM’s and that’s basically the only way. If you lose the medivacs or too many marines, the zerg can instantly drone to like 80 drones and then you’ve lost. Critical mass basically, unless they’re really bad. Other than that, 2-1-1 works due to the ability to outmultitask, if you can’t outmultitask your opponent you’re severely behind because it’s borderline all-in. Not enough army, not enough workers.
If you run hellion opener, do not trade your hellions for drones, A drone run-by is always risky, you’ll leave yourself exposed to ling counter attacks if you lose your hellions. Just circulate and kill creep, if they’re exposed, then ofc dive and kill some drones, just beware that you should pull back before you lose anything. It’s better you get 2 drones and keep your 4-8 hellions than lose all of them for 10-15. Because then you’ve got nothing at home at you’ve likely also overmicroed. And then GG zerg imba threads come
Aside from that, 6-8 medivacs is golden, if you’re dropping, if they have mutas scan ahead or know where they are so that you can safely drop.
LBM(ling bane muta) -> Go mines
RR/RH/HL/LBH -> Go tanks (Roach ravager, Roach Hydra, Hydra lurker, Ling bane hydra)
When attacking your opponent, always remember to pre-split your marines vs banelings, and poke with 5-6 marines and a medivac to the hatcheries or whatever, with tanks sieged + covering with the rest of your army pre-split. With a presplit, you’ll basically always trade super well, and they have to take a fight on your terms. They send a few banelings, you just snipe em, They send a ton? Just run back into tank fire. They engage fully? Then you have tanks + stimmed pre-splits, even with surround that aint pretty. Otherwise, you can pickup + just leave or if they don’t engage you’ve sniped the base. Basically always a win.
Aside from that, Kite banelings off-creep.
If they’re speed + in high quantity or on creep (espec with speed) you gotta split.
basically all I can think of man, if you want some more help, always happy to help
Mabadi#2380 NA or EU although I’m only on NA really. Just hit me up and I’d be happy to help <3
Happy hunting!