My tailbone hurts after sitting in my desk chair?

After moderately long gaming, writing, or binging sessions, around 2-5 hours, my tailbone always hurts. I never had this problem before with any of my other chairs and I'm using a chair very similar to my first. I'm using a wooden chair from an old dinning set. I have a good desk chair, but after I transplanted my computer from my basement to my room I decided to leave the chair down there because it would barely fit in my small room. I was wondering if I should move my chair or if I should just put down a pillow or something until I can afford a new chair.