Well done Op on wanting to be healthier!
I'd recommend:
Buy 9if you don't already own): Kitchen scales, running shoes, sports bra, cheap trackys and tshirt. Smartphone (able to download apps) and headphones
Download My Fitness pal and COuch to 5k
Put EVERYTHING you eat into my fitness pal, you'll soon see where you are going wrong. Once I started weighing food I was absolutley gobsmacked at the 'recommended portion' or cereal! I was eating 3-4 times the recommended amount, and thinking I was being healthy, because all I'd eaten was a bowl of cereal for breakfast.
Then, go out and do the couch to 5k. I'm not going to lie, it's hard at first. It's a series of podcasts, in the first week you do a 20 minute run, with 60 seconds of jogging, followed by 90 seconds of walking, then build up from there. It hurts, and it's a bother, but it works. Your back pain may be due to excess weight, running may actually help it. The thing is though, you have to decide that there's no way you are not going to do it, and go from there.
Feeling fit is a wonderful feeling. Think of how good it'll feel to be fit, lose weight and be able to run!
Good luck!