Knee injury? ACL tear? Not sure what it is? Help please(:?

Not sure what to do, I have injuried my knee last year and track, and I had a MLI strain. I now play volleyball(4th year playing) and I dive alot and this season my knee has formed a bump, on the side up to the right of my knee cap, now it has gone down because I haven't been playing for a month, but I have now noticed a slight popping when I move my knee and I every once in awhile get sharp pains in it. I have talked to a coach at school who is also a EMT and he didn't really say much about it, he said i probably just bruised the bone and I'm not going to go to the doctor if it's nothing. But I wonder if it may be something? My mom says to wear my brace that I got for my knee when I Hurt it in track 2 years ago, but I am afraid I could injure it more. I have searched injuries like this and I have a ACL tear, but my pain in popping is a lot less painful and loud.