Gaining too much pregnancy weight?

I am currently 18 weeks pregnant. Before getting pregnant I was already obese. I’m 5’5” and I weighed 225. I wasn’t extremely active but I had lost weight after starting my last job going from 300 pounds to 225. I was able to keep the weight off until this past winter. I was 230 pounds when I found out I was pregnant in February. When I notified my job that I was pregnant at 12 weeks they fired me and I’ve been depressed and way less active than I was. I went into my last doctors appointment at 16 weeks and I was told I weigh 240 pounds. This alarmed me since that seems like a lot of weight in just an 8 week period. I’m worried I’ll get back up to my 300 pound weight and risk the health of my baby if I’m not careful but how can I keep my weight under control with constant cravings and not being able to be as active?