I suggest buying the books Pain Cure RX. and Overpower Pain by Mitchell T. Yass
I tried rolling on a baseball and I don't know maybe helped a little. And I can do some back exercises, my back is not weak, not very strong but not weak.
MRIs really don't tell you much about muscles -- it's really more about soft tissues that don't show up on X-rays (bones show up well on digital X-rays). In your case, most likely there's something in the way you're moving that's not going well -- such as tight hips, lack of mobility in the joints, and the like. There also might be some hydration or nutrition problems, which would explain the hamstring problems. So might not stretching enough -- doesn't have to be static stretching, could be dynamic stretching such as yoga, but you could just be very tight. Stressed out people are tight. People who don't sleep well can be tight. Some people have body parts that are odd -- I have a twisted pelvis that's just the way I'm built. These kinds of things usually don't bother you when you're young, but over time they get us all because we're all odd somewhere. There are few perfectly shaped people. Sprinting is one of the most traumatic things you can do to your body -- doing it occasionally when you need to get somewhere quickly is natural, but doing it over and over isn't, and this sport is notorious for muscle cramping (hamstrings, anyone?), foot injuries, ankle injuries, etc. Look at any Olympic sprinter and then look at injury history -- for most of them it's a pretty painful pursuit. What I would do is find a sports chiropractor or really experienced cross-fit trainer or sports osteopath or someone who works a lot with athletes and have them watch you run. They can then tell you if you're moving properly. They can also test your hips and knees and legs and see if they have sufficient mobility in every direction and, if not, give you a program of stretching and strength training that will improve you where you're rigid. That might help. Also know that any injury causes you to compensate for it, and that can create incorrect movement. It's pretty classic for serious athletes to get hurt on one side of their body one year and the other when they come back because the better side compensates for the weaker side. This is especially true if you've used painkillers or steroids to keep going or gotten surgery -- you're never the same after surgery or as strong as nature made you so you have to exercise knowing that. All this is stuff I've been told as I've gotten older and started suffering lots of pain after having been an avid basketball player, runner, and martial artist for years without major injury of any kind. It got me anyway partly because of all the reasons I mentioned. And on other thing -- sprinters do a lot of bending, and just the repetitious act of rising back up wrong can account for an injury on one side like you're having. Get evaluated by someone who does it for a living and see if what they say makes any sense (some are just clueless, so don't turn your common sense off). Good luck.
did you try with exercises?