Does anyone know what kind of hairloss this is? Hair thinning on sides

[baldingonsides]

My hair has been considerably getting thinner on the sides and has now reached this state, i've been to the doctors to get my thyroid tested but they found nothing and other blood tests they said were fine. Both left and right are like this and have been thinning for about 5 years, I'm 24. My hair at the top/front isn't receeding but has lost some density/thickness but not anywhere like the sides, not noticeable at all.