First question, It may be a muscle that is sore in that area or if it injured in someway it could be an internal bruise. Example if your arm was squeezed or bumped against something. It could also be bursitis, if you do any type of repetitive movement with your arm. Another cause could be Tendonitis, which could be inflammation of the tendon in that area. Without an x ray it would be hard to see what is actually going on in that area. Since this has been going on for a few months I would make an appt. and have that area checked out by your doctor.
The medication that you are on does cause vaginal dryness, you can try a lubrication which should help. There are several on the market. Astro glide, KY, just look in the personal hygiene area of your store.
Hope this helps and gives you some ideas, If you need anything else please feel free to ask. If you found this helpful don’t forget to click the *accept* button!