I am 26 years old and I noticed like 2 weeks ago when I was getting my hair cut there was a large lump on my head I thought it was my hair cut but the other day I really took a good look and asked my girlfriend and she agreed that there was a large lump as well like the size of my hand cupped does anybody know what it could be? I'm worried

Are you sure it was not that way all your life?
Does it feel tender, sore, swollen, unusual?

Sounds like a sebaceous cyst...