So, first, see a sports doctor, chiropractor, some other kind of specialist to check you out. FWIW, I had a similar series of injuries, and I finally discovered that I have a curve in my spine that meant that running messed up my feet, knees, hips, back, shoulders, you name it.
Second: core strength and flexibility. Seriously. Big, big difference.
Third: I agree with others that, far from being a wimp, you are pushing too hard. As we get older, our bodies start telling us that we can't do what we used to, but our minds think we still can, and the result is injury (note that this is especially true for "real" athletes, because those are exactly the people who are used to pushing through pain). I have seen this happen with several men in their early 30s, and it happened again with me in the late 40s. I am unfortunately a binary type of person -- I go 100%, or nothing. When I had to stop running because of those repeated injuries, I did nothing and gained weight/lost all fitness. Then I started Crossfit, loved it, and threw myself into it -- and, boom, here come the repeated little nagging injuries (I mean, I even tore the cartilage in my rib cage -- who does that? And two weeks after I came back, I did it again on the other side). UGH! I started to think, damn, maybe I'm just meant to be out of shape and fat. But then I finally just told myself that I am old and out of shape and need to suck it up and not go so hard so fast. So I took a really slow approach back, even though it drove me batshit. And now I am up to 5-6 days/wk with no injuries (knock on wood).
But the other key: paying attention to my body's signals BEFORE I get injured. Just last week, I was doing power cleans, and my back just kept getting tighter and achier -- nothing immediate or sharp, just a dull tightness that kept getting worse. And I quit -- I realized if I kept going, it was going to spasm, and I'd be laid up for days, if not weeks. Never done that before, just quit in the middle of a workout, and boy did it feel horrible to be sitting on my ass while everyone else was suffering. But I spent the rest of class stretching, took the next day off, and then the day after that made sure to avoid back/pulling work. And when I came back the following day, I could do snatches with no pain. So I basically missed one day instead of a week or two (not to mention the raging pain and inability to move. So, you know, yay.).
Tl:dr: You basically need to suck it up and not be a badass every day. Spend twice as much time stretching as you think you need to, do lots of core work, and back off when you feel pain. Injury is not the kind of "pain" you need to push through.