how long should you go before you should be able to increase the weight, im guessing if you are able to increase it, that means you are making gains. i just realized ive been doing the same weight and exercises for my biceps since april, this is pretty bad as far as gains go, shouldnt i be able to do more by now?

dumbell curls 4 sets 35lb
barbell 3 sets 60lb
machine curl 3 sets 60lb, 70lb, 70lb

only thing i increased there was the machine curls, doing 10 extra pounds on each set.