Take it easy at first: it's normal that some parts of your anatomy hurt because your core muscles needed for cycling are not very developed yet. You may also be leaning too much on your arms and not bending your elbow enough...

However, elbow pain can indicate tendonitis and you don't want to go there. Last year I had excruciating pain in my left elbow, it was really killing me after my first metric century. It started by 3/10 pain after my first 60-ish rides but was greatly increased as time in the saddle piled up. I went to the bike shop. Turns out that, according to the charts and to the length of my forearm, my stem was already too short, but we still brought the handlebars one hair closer (by flipping the side of the stem, which has some angle to it) and after that (and a few days of rest to let the pain subside) I was fine. So fitting only goes so far.

When I started longer rides this February I had some pain between the shoulders again - time to rebuild those endurance muscles - but never anymore elbow pain.