Gym questions?!

Hello ladies!! I have a question and I feel silly asking, but here it goes. I am 11 weeks pregos and I would like to start going back to the gym reason being I want to stay healthy and active plus I've gained some weight! Before being pregnant I was at 137 now I'm up to 145! Not good I know! I think mostly the weight is coming from my breast for they have become rather huge! So question is what all can I do at the gym? I've asked my dr and he said walking is al I could do! :-/ is there more I could do besides walk?! TIA 😊