Of course you're not the only 'weak' one in there.
not everyone at the gym is a six-packed young guy. there are people just like you there, trying to get muscle and maybe lose a little weight.
A personal trainer may be optimal for one who is confused as to what to do. In your situation, I would recommend it. If you're new to the experience sometimes it can get overwhelming, and you could under-work/overwork your body. A personal trainer costs money, but when you lose that weight and gain muscle, it may be worth it.
You need to give your body rest. If you go to the gym every day, you'll only wear your body out faster. Muscles get bigger by repairing themselves after they rip (which happens every time you work out). Give them a day or two to repair-- if it's sore, it's working. =D
I say go very light the first time you're there. You don't need to rush into it... get used to the equipment and the atmosphere. Nonetheless, get used to how your muscles and mind works there.
sorry for the lengthy answer.
Hope I helped though.
