I am a 21 year old female and my hair is thinning more and more.?

I recently have been noticing my hair thinning alot more this year than others. It is only on the top of my head I get sunburnt on it and I am scared to dye it anymore. My hair has thinned significantly from how it was in high school. I thought it was from getting highlights and dying it now and then but I didn't do it that often. My mom has thick hair and my dad didn't start going bald til his 50's what is wrong with me? The doctors said my thyroid is normal and I"m not anemic. I am on a birth control which i started when i was 17 and an anti-anxiety medication. This is making me so self concious. please help.