My hair has affected the way I look?

Not meaning to brag but before I dyed my hair black due to the fact that It was turning really unhealthy looking because it was too light and it has also became very very thin, I thought I was quite a pretty natural looking young girl I didn't wear that much make-up as such but now my hair is actually disgusting it's dryed out, thin and when I wash it it becomes greasy quite quickly I always have people in my college s or saying snide remarks like I don't wash my hair when I made it quite clear to them that it was damaged and I have to put on very dark make-up because my hair is that dark, I was also considering hair extensions Im starting to feel fake and I don't like it, is there anything I can put on my hair to try and thicken it out and make it healthier looking? Thanks to anyone who helps sorry it's long ! N.