If you are small and want to be big you are probably mistaking the workout u need to do. "No pain, No gain" often leads to plenty of pain. Believe me. You need to do the cardio, and you need to ease your way into weights. Hitting them really hard is not only really stupid, but you will wear yourself out and are gonna do yourself some potentially serious harm. Start off with some light reps, maybe 8 - 12 with some weights that you can lift easy enough, but by the end of your set you are pushing yourself to finish. Do this for a while, take Creatine and some protein powder. Eat lots of meat and carbohydrates. Keep this up as a general rule for the workout for the first month or two, then gradually add more weights to the reps until you find yourself forcing the final reps again.
No pain No Gain was invented by people who don't know what their talking about. Pain is bad.
Also, get someone to spot you. If you overdo it and are going to drop them you may need someone to help. My brother was doing some overhead presses and didn't have someone to spot him, he ended up in trouble and dislocated both his shoulders because he didn't have that spotter.