I have a DVD called "Body by Trimester" by Joy Southworth, she gives you an intense workout in 30 minutes and it s tailor made for pregnant women. Check it out on amazon. good luck!
http://www.amazon.com/Pregnancy-Fitness-Dvd-Trimester-February/dp/B0079QDAFK/ref=sr_1_1?ie=UTF8&qid=1379948225&sr=8-1&keywords=body+by+trimester

I like Lindsay Brins' DVD for pregnancy. Some people aren't a fan of her personality, but she doesn't bother me and I like her work-outs. The package includes different DVDs based on trimester.
http://www.amazon.com/Lindsay-Brins-Complete-Pregnancy-Workout/dp/B000YA4F2K

Did you talk to your doctor about the back pain last time? Generally you are good to go, but if you have pains ( not sore muscles, but real pain, especially in your lower back) you need to discuss with your doctor. Water exercise, like swimming and water aerobic is really great if you have back problems.
If the doc gives you green light, tell the instructor before class that you are pregnant. That way they will keep an extra eye on you and let you know if you're doing something wrong. ( most often the reason to later pain)You also should not do any exercises laying on the back, like crunches, after week 12.
Good luck!

I had a lot of discomfort in my back during the last part of my first trimester and beginning of my second. Invest in a good support belt and it will help tremendously. Once I started wearing one during my workouts, the pain was greatly diminished. I'm 30 weeks now and am able to exercise almost everyday. Of course, listen to your body and stop if you are in too much pain. AND talk to your doctor if it gets worse or continues to plague you.

I am 11 weeks, and was just at my second appointment this past friday. I asked them both times about exercise just to see if i got different answers from different midwives. This is what i have been told so far. I am not sure if you have heard of Les Mills programs but I was doing Body Pump and Body Combat before I got pregnant and the motto is that you can still do these things within reason. They told me to listen to my body. As for the Body Pump class the first lady I saw actually takes the class. She told me that its great for me to continue with, with no weight restrictions until they tell me otherwise. As for the Combat class and any other cardio class in general like zumba they want me to be able to carry a conversation while doing it or keep my heart rate in the 140 range was what the second midwife told me. She said if you get yourself too overheated then your body is focusing on cooling you down and it takes away from the fetus. They told me ab work was fine however crunches usually end up stopping between 14-17 weeks because your belly just starts to get in the way. But planks and things like that are okay as long as its comfortable. Main thing is listening to your body. I am actually going to try out Combat tontie and Zumba this weekend for the first time since I have been pregnant. I didn't feel like I had the energy to do a class because of 1st trimester fatigue so I was just working out on the ellipical. Good Luck!!