As others have said get an exam by your doctor. After you get the all-clear then we can work on the problem at hand.

Assuming no medical issues we can chit-chat regarding physical conditioning, riding position and bicycle set up. I think it is great that you want to get in better condition which will improve life in general. This is not a bunch of old guys saying "get a physical" rather it's a group of bicycle enthusiasts who advocate priorities and the number one priority is to make sure you don't have any underlying health issues that might be simple to correct now but difficult later.

I spoke to my PCP right when I was getting started with more intensity then what i was doing and he really fell over backwards to make sure I was up to it. And the last time I was in his office he told me that he wished he had more patients like me who are interested in their fitness. No one ever said late in their life that they wish they didn't have so many physical exams.