Exercising while Pregnant

Danielle • Dated my husband since December 2006 and we were married May 2016. Baby boy Henry born June 2nd 2017 👶🏼💙
Hi ladies! ✨Happy new year to you all!✨
I am in my second trimester (almost 16 weeks) and I just got cleared by my doctor that I DON'T have placenta previa and that it is safe to exercise. 
My question is, what types of exercise are safe to do with my planet fitness membership? My doctor just said no exercises where you "bear down" like pushing weights with your legs and things. But that's all the info I got. 
I really want to make this a daily or 3x a week thing for my health, the baby's health and a mood/energy booster and it would be a bonus to tone my legs, arms and butt. (Not looking to get fit though of course while pregnant). 
Also, how do I do this without losing weight? I want to keep gaining the 1lb a week my doctor said I should gain.
Please let me know your experience with this, thank you!