Does anyone know if I can start to exercise while pregnant even if I wasn’t previously active?

I heard that it’s not a good idea. This is my third baby and after my second I was going to start working out but I waited a year and then I got pregnant again. So now I’m pregnant with my third, and worried about my body this time around due to it being so weak seeming. I’m scared I will have more pain because of it. Especially in the pelvic area. I’m 16 weeks and already having shooting pains in my crotch if I move wrong which usually happens in third trimester right? I didn’t feel this until my belly was way bigger and heavier last time. Worried I won’t even be able to walk because last preg I could hardly get myself out of bed with out shooting pain in my crotch and doctor said it was normal.

I lost A LOT of weight after I stopped breastfeeding. I got very thin, and I noticed my skin feels much looser then the last time I was this weight, and my muscles feel weak. I lost my butt, it’s now a pancake lol. I want to work out but not sure if it’s a good idea.