Not many people would recommend a dbol only cycle. When you say weak, do you mean tired or you are just not getting stronger. How long have you been on them?
At 30mg/day, you should start to notice a difference in as little as 5 days. Or at least I did. Endurance went up, felt more enegetic. For me, I went up 4 pounds the first week (water retention) and muscle pumps started to build. By the second week, muscle pumps were in full force and small but noticeable increase in strength.