47 Year Old Male Weight 220, Never Had Constipation Before.

47 year old male weight 220, never had constipation before. Have hypothyroidism for over 20 years. Normally ride bicycle to work 18 miles each way. I have been riding to work for over ten years without issue. Did double red blood donation on Thursday and then rode home like normal. Then stayed home Friday. This is the first time I did a double red blood donation. I had constipation and constipation Friday then painful constipation today. I did take fiber gummies after constipation. Since it is the first time I have ever had painful constipation, I don't know if I should wait a few days or try to go to doctor tomorrow.