I agree with the above posts. You need to pay more attention on the form and less on how much you can lift. If you execute an exercise correctly, then you will not need as much weight. As Karin suggested, a good idea might be to hire a trainer or ask a trainer at your gym (if you belong to one) to show you how to perform your exercises correctly and help you figure out the right weight for you to lift. Trying to lift more weight is not always the best way to go about it. Try to lift smart and you will see faster results and you will also become more efficient. You have your whole life ahead of you to gain muscle and get stronger. Be patient and learn as you go.
I hope this helps.