Stretching should be done after working out, not before. That may be part of your problem depending on how you are stretching. As a general rule dynamic stretching before, static / assisted / pnf after the work out.
This is one of those things that I'll disagree with no matter what they say. If you look at what a muscle pull is, you'll find that it's an overstretched muscle or torn muscle. What qualifies as an overstretched muscle depends on how flexible you are. If you don't have enough flexibility to do the activity then you are more likely to tear or pull your muscle if your muscle goes beyond the limits. One of the things that we always say in my school is to not kick higher than you are able. Kicking higher than you can comfortably kick is the same as overstretching the muscle. If you kick too high then it will tear the muscle. The muscles tears because it beyond the limits of its flexibility. The more flexible you are the less chanced you'll be injured as a result of limited flexibility.
The article below is from web MD
Should You Stretch Before Exercise?
Not necessarily. It's not proven to help prevent injury, curb muscle soreness after exercise, or improve your performance.
Static stretching before exercise can weaken performance, such as sprint speed, in studies. The most likely reason is that holding the stretch tires out your muscles.
You should warm up by doing dynamic stretches, which are like your workout but at a lower intensity. A good warm-up before a run could be a brisk walk, walking lunges, leg swings, high steps, or "butt kicks" (slowly
jogging forward while kicking toward your rear end)."
I think the problem is in this statement: "It's not proven to help prevent injury, curb muscle soreness after exercise, or improve your performance"
When I'm stretching I'm trying to improve flexibility. If I can improve my flexibility then I'll be able to improve my performance.
If I improve my flexibility then I'm less likely to be injured as a result of not being flexible enough. I can't improve my flexibility unless I stretch.
I don't stretch to prevent from being injured. I stretch to become more flexible.