Today I noticed a gradually growing ache in my right knee. Normally, my knees are slightly hyperextended, so after crossing them for any amount of time they hurt. However today I noticed this pain while walking and it felt like it was more in the tendon/muscles behind my knee joint, I've tried my normal remidies for pain relief (walking around, and then when that didn't work I rested it for a few hours), with no results. With no movement the pain is probably at a 2/10, more of a discomfort and goes up to about a 7/10 with lots of stiffness while moving. It's slightly swollen but no visible bruising, and I have absolutly no idea what could be causing it. I'm an 18 year old female, so I don't think any age-related ailments would be the cause.
So my question is if this is something I should have checked or if it's anything I should be worried about?