Good diet? 120-130 grams of protein? I take it you're four feet tall and weigh 70 lbs or so?
Oh, you aren't? Well, there seems to be some room for improvement here...
Other than that, I never liked those 5x5 things for bench at all... Works ok for squatting, but then again, just about everything does...
Do you feel any discomfort when benching? Around the elbows or at the shoulders?
And... You're 19% bf? Where'd that measurement come from?
You also seem to be seriously lacking in the back and delt department tbh... Tris too, really... Personally, overly simplistic approaches to upper body training have never worked for me... I can pretty much do 2-3 exercises for my legs and keep getting stronger, but upper body always needed a lot more variety (not necessarily volume per movement or super-high frequency) than what a typical 5x5 routine provides.
Can you give us any more info on your issue... When exactly did it start?
If we can't find out what exactly is at fault, and going back to eating a proper strength training diet doesn't help... Then I would just start over (new program plus diet, maybe even focus on incline instead of flat, etc).
Also, dropping the weight by only 10% and working back up may work sometimes, but it's imo way too little of a difference.