Sam my man,
There could be several reasons for this. Your training, which is important no doubt, is probably NOT your biggest cause for not growing. Most likely it has to do with your diet and your recovery stages.
Keep in mind, if you workout for 90 minutes, and sleep 8 hours, you really only spend 5%-7% of your day in the gym. That should tell you that what you do outside the gym has EXTREME effect on how you build muscle. Enter diet....
WEDYEY? What, exactly, did you eat yesterday?
Basically, if you are serious about this whole thing, of gaining muscles, you have to be serious about all aspects of it. Training is great, but it's only 1 part out 3 that yield muscle gains. You have been focusing on this 1 part, but neglecting the other 2, well guess what, you're going to lose confidence because the results you see are going to be minimal and shitty. I definitely don't blame you for losing confidence. Now is the time to do something about it.
So... what should you do? Well, there is almost no doubt in my mind you are going to want to optimize your training routine as well, but you really need to:
1) figure out how many calories you need daily, just to maintain your current body-weight. - Take your body-weight in lbs, multiply it by 10, then multiply it by 1.3 - 2.2 depending on your activity levels... so most likely around 1.6.
2) You need to add 300-500 calories to that amount, so you can be in a caloric surplus. Being in a caloric surplus is the ONLY WAY to gain muscle... no matter how many exercises you do in the gym, if you aren't in a surplus, it is SCIENTIFICALLY impossible to gain weight.
3) You need to figure out how much you eat on a daily basis... Lets assume you need 3000 calories to be in a surplus, and you only eat enough food that amount to 2500 calories every, single day, what do you think will happen? Will you see your body grow...? No.
- Figuring out how many calories you eat on daily basis sounds a lot harder than what it is. It does require for you to read a little bit so you can learn how to do it, but it's extremely useful. Think about it, you can use science to make your body grow, why wouldn't you? It's proven to work.
In conclusion, if you don't feel like doing any of those "food related" things, you could just eat as much as you possibly can. That still doesn't guarantee that you eat enough, but if I can make an assumption, whatever you're eating right now, is not enough... otherwise you would be bigger, get it?
So, if you want further help, you need to list two things: How you train, specifically, what routine you use and how many sets/reps, and you need to list what a usual day of eating looks like.... In case it wasn't obvious, the more honest you are, the better. Remember, this is a science...so if you fuck up the numbers, you will not achieve the results you want.. But if you do everything accordingly to plan, you WILL have the body/aesthetics you are looking for.