i'm a lifting n00b. i've only been lifting (strictly) for ~ 2 months. i can't seem to increase my #'s. for example, i do my benching 5x5. whenever i get to my 5th set, if i could only do 3 the previous week, i STILL can only squeeze off 3. should i try moving ahead to a heavier weight or keep benching until i can finally get 5 off?