This should not be a muscle strain, but a symptom of severe muscle discomfort caused by sudden excessive exercise when you just started fitness.

You need to keep exercising, but you need to reduce the amount of exercise and give you time to adapt. After this recovery, gradually increase the amount of exercise, and the pain will be gone. But if you rest completely now, the pain will recover in three or four days, but once you get on the spinning bike, the problem comes back.

You don't need to see a doctor at all!