Bob's right. IT ALL Depends. And you'll get stronger running with weights on your ankles, but it can also ruin your knees! But you are new to the group, so it's no surprise you're the one off the back. Glad to hear that deosn't discourage you, though.
Your bike may suffer from lots of things, weight being a major one. Level of quality, state of tune, and overall fit also play a large role. I'd keep riding it until you need/can afford a new one. Meantime see if you can get a friend to loan you their lighter model; somebody your size. Then try out a couple others too. Talk to your buddies, and maybe get one of their bikes cheap when they buy a new one. This will give you a chance to get up to speed on things before you spend too much money in the wrong place.
In answer to your question, weight does matter a great deal, especially if you are small like me. A pound or two isn't a big deal, and fitness makes the bigger difference. But if your bike felt twice as heavy like you said, (which it could be) then you are at a huge disadvantage to the others. They'll enjoy it until you get the right ride. Then you'll be the one waiting on them!
Meanwhile, keep truckin'! You're going to be great! Good Luck, TT