Should I see a doctor?

Recently, I’ve been feeling super off. I have randomly been getting super lightheaded. I’ll just be walking and all of a sudden it feels as if I’m going to fall over. Just two days ago, I started having trouble going up the stairs at my house. I can barely get up 5 stairs without feeling like my legs are going to give out. I usually can walk up all 14 with no issues whatsoever. Right now, I feel as if I could literally pass out on the floor. I had a good sleep and drank water. So, I don’t think I’m dehydrated. I’m 20, if that means anything.

I took a pregnancy test and it came back negative. I haven’t changed anything in my lifestyle. I just don’t really know what’s wrong with me.