Exercise question... Please help!

I love to exercise and obviously do it too much because I keep injuring my hips. There was a time I was riding 16 miles a day and doing at home workouts such as push ups, sit ups, etc. I even have Jillian Michaels workout videos. But I can only do so much. Just the other day I was in my classroom (I work with school-age kids in the summer) and we were doing our exercises and I had to show them how to do a proper sit up. I did 10 of them and I haven't been able to walk right since. I have no idea why that affected my hip like it did, maybe I got up wrong afterward but I literally walk like Dr. House and have been calling myself a Gimp ever since. I feel useless and lazy and I hate the pain. X-rays show nothing so it's not bone related. Planning an MRI to check for other causes but I don't want to stop exercising! I need something I can do that still will burn calories but not be too hard on my joints. I do have Crohn's related arthritis and deteriation of cartlidge from years of steroids and other health issues. So I'm a pretty old 32 year old but mentally I can not allow myself to follow suite with my body. I'm trying my hardest to fight this. I was a heavy girl when I was in my teens (it seems to be a genetic thing, mother was heavy, brother and sister both heavy to this day, etc.), but lost a lot of weight really fast due to Crohn's. I now fluctuate between 150 and 165 but that is still overweight for my 5'5" self. I'd like to be about 135-140 area to feel a bit more comfortable. I'm trying to make any drastic changes but I want to try to be as healthy as I can be! I'm working towards starting a family, I have my wedding in January, and we really want to have children together. I have a 50/50 chance of having an easy pregnancy, I figure keeping myself as healthy as possible will increase the odds in my favor. Soooooooo, very long story and I apologize (I tend not to shut up when I should make a long story short) but does anyone have any easy exercises I can do while my hip is healing from it's latest trauma? I gain weight when I look at food so I'd like to keep working towards my goal any way possible! Any advice would be very much appreciated! Thank you in advance!