Can’t lift leg up in sitting position

I’ve been having problems with my left knee and saw an orthopedic after having an mri done and he didn’t seem worried at all. I’ve been having more pain/discomfort in it than usual and noticed when I’m sitting I can’t lift it up to straighten out in front of me like I can with my right.

I hate to go back to my doctors because I’ve already seen them numerous times for it and since the orthopedic didn’t seem concerned at all, I’m not even sure if it would be worth it.

Could there actually be something wrong with my knee? I’m starting to think it’s all in my head.