Underweight? Thyroid?

Im kind of concerned I have something wrong. I eat 2,400+ calories a day. But i bike everywhere and work out at gym. I swear its all i can fit in my tummy per day. Plus protein supplements! I've heard a lot about thyroid issues in the news lately. I dont have insurance, so cant just go get a bunch of lab work done on a hunch. Im 5'4" 105lb 33yo. Has anyone else gone through this?