I have been going gym for about a month and a half and i have seen gains on all excerise i an lift 18-20kg on incline using dumbells. But on bench press i can only do 12.5 or very few reps of 15kg a side.

How come i have not been able to see any gains on bench i am not expecting miracles over night but its a bit confusing as i can lift more with dubells and not bench

Thanken you