The issue with you might be something related to the chemotherapy you had some years ago. Chemotherapy is a treatment which can cause damage to blood vessels. This causes blood to clot. In groins and legs, blood vessels are pretty large. Clots occurring in those areas may result in severe pains as you may suffer now. There can be some other reasons for this pain. So it is better to get it investigated first and follow the instructions of your doctor. A doctor can easily find out the reason of pain. It should not be put in a delay. Get a medical attention as soon as possible and get checkups done at the earliest. It is better to be safe than sorry. Good luck.