For the past month or so, I have been doing 4 sets, 20 reps with 25 pound dumbells, by the end of this time frame I was able to complete all reps, and all sets without any need of extra momentum for the last few reps. Now that I started doing 30 pound dumbells(which I started 2 days ago) I cant even complete 15 reps, and I am only able to do 3 sets, because my biceps, and full arms get soo tired from holding the weights and repping them. Do you guys have any advice on how to overcome this difficulty, and being eventually able to do the complete sets and reps. Because I will be frank that before the 25 pounds, when i was doing 20, the addition of 5 pounds did not affect me to the magnitude of jumping from 25 to 30 pounds.