Stretching outside of knee?

I’ve been playing soccer for the past four or five months every single day, alot more then I’m used to. At the beginning of our training during the summer when I was pulling the back of my leg up to stretch my quad I hear a pop and ignored it. A couple days after I got this terrible pain in my knee where I could hardly walk or move it. But I went running and I felt alot better. I get these bad pains every once in a while. But now my knee pops all the time when Im stretching, and when I stretch it I have this bad pain in my thigh. Can anyone give me an answer for how to fix this, or stretch it?