If my seatbelt was not buckled when the driver of the car I was riding in caused an accident that injured me, can I sue for damages?

Yes, you may. What happens here is an issue of comparative negligence, meaning did you cause or contribute to your own injuries by not wearing that seatbelt? That’s a medical decision. That’s a biomedical decision that can be proven by experts, but just because you were not wearing your seatbelt does not bar you from making a claim.