I would cut back the number of sets.......you do not need to do 20 sets for pecs,try working harder and doing 12 sets.
If you want more size,try this routine..it`s not designed for strength but will attack your pecs in a way that you`re probably unaccustomed to.
Pre-Exhaust Super-Set:
{Flyes:
3 x 10 (constant weight)
{Bench Press:
3 x 8-10 (constant weight
No rest between exercises,one minute rest between Super-Sets.
Smith Inclines:
3 x 15,12,10 (next week do,3 x 10,8,6.....alternate rep schemes weekly)
Paralell Bar Dips:
3 x failure-bodyweight only (after you can get 20 reps per set,add a 15 pound dumbell around your waist)
Rest no longer than 60-90 seconds between sets on the last 2 exercises,keep it intense and leave the ego at the door...............mind/muscle connection focusing on stretching and squeezing the pecs,not poundage.