1 word....Plateau time!
we all go through it, and it sucks. there are a lot of things you can do to break this, but the first thing you need to get into your head is that EVERYBODY hits plateau's and they suck! so dont get discouraged! here are some things you should consider trying out:
Change up your workout/ check online for new exercises to stimulate different muscles, try something new dont get to repetitive.
There are some supplements out there that can help you through these plateau's too.
Also you sound like you've been training balls to walls 4 days a week....dont overtrain. take it easy and let your body rest a little bit, maybe take a week off and eat right, and just rest up. the more you overtrain your body..the weaker it will get. 110% everyday will eventually lead to catabolism.
There are plenty of different workouts you can choose from to stimulate muscle growth, try this one out...rest up before you try it and let me know! if you have any questions just PM me!
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---try this workout