Maybe just some stupid suggestions but:
1) diet is very important. Don't try to push your calories over the border. But make sure you get in 2 grams of protein per kilogram/0.8 gram of protein pound of bodyweight. For fats and carbs: on training days, eat more carbs, play around with this. Given your body comp, try to get as much carbs in as protein. If you get fat, eat less, if you feel tired, eat more.
For fats, eat around as much fats as protein on non-training days.
So to give an sample (can be different for you): on training days protein/carbs/fats: 30/40/30
On non-training days: 30/30/40
2)Well, you said you use the same reps and sets for 1.5 year. That is quite a long time! I hope you added weight every 1 or 2 weeks.
But to be honest, I can really see why you don't gain mass anymore. 1: you probabely aren't getting very strong on this program. Being strong is a really good base to get bigger. 2: this is pretty much a "smart bro-split". It certainly isn't stupid, for a pure bulking program, it's pretty decent!
The problem is, you can't really get stronger at a more advanced point if your stuffing all this extra stuff in.
Try this: https://www.T-Nation.com/training/complete-power-look-program
You have built mass in the last 1,5 year, now is your time to get strong enough for this mass.
To get say it as simple as possible:
-take like 6 to 8 weeks of doing 1 heavy main lift everyday, (a variantion of the folowing: bench/deadlift/squat/Overhead press), like ramping up to a 3 RM (not a personal maximal per se). Use the same main compound lift every week during this phase!
- Do accesory work to fix weak points, and do pull-ups and rowing to balance the pressing.
-Don't do anything like calfraises, biceps curls, tricieps extensions. No fluff, just hard work on the basic stuff.
-When you have done this, go back to your old program. See what happens.
- Sleep like a baby 8 hours a night and don't stress. Recover!