Off the Couch

I have been told countless times by Drs and family members that I need to be physical active for my own good. For as long as I remember I have made countless exercise schedules since I was in my early 20s and have not been able to keep it up for more than 2-4 weeks. When I started the Gluten free diet I feared that I would fall off the wagon too. However, I have been pretty amazed on how well I have done in the last 1.5 years on GF diet. I have not given in to the temptation of bread and pastries not even once. Not only GF, I have given up most processed foods, caffeine and sugar with little difficulties. So why can't I stick to an exercise regime? I guess part of it is that I am always tired but I know this is not an excuse. However, during the years when I didn't know I had Endometriosis a 30 min work out will leave my back in such a state that I disliked going to the gym. My recent plan was to walk for 30 min every other day and I probably have done it may be 4 times in the last 2 months. For some reason there is always an excuse for why I can not get off the couch and start moving. Any one reading please suggest any ideas that helped you stick to a schedule. We are not talking about hard core exercise here since my body can not handle any strenuous work out at this point.