During practice last Thursday I was praying throwing a metal ball for shot put for track and I think I pulled something but I didn't think nothing of it but I kept hurting . And then later I found a lump but feels like a knot on my mons area and I haven't had sex lately and I'm nervous because I don't know what it is and it hurts a little . What could it be ?

If it is not a muscle that has cramped to the point of making a lump then your best off going to the doctor to see what is going on. Muscle is usually suspended between 2 points and a tear or complete detatchment can caus a lump to appear because the muscle is no longer stretched. You need to get checked out as this type of injury untreated can have ramifications for the rest of your life. Please see a doctor (sports medicine preffered) when you can as soon as is possible.

But if it's a muscle why would that knot or lump feeling be near my vagina but it's under my skin. it's not big but not small neither .

Do a search on muscular anatomy. You will see a lot of things come together at that point in your body. When throwing shot almost your entire body is involved. It is something that can't be diagnosed over the net. You need to see a doctor to confirm it.