Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine you and obtain a history, I can not tell you what the exact cause of your symptoms is. However I will try to provide you with some useful information.
I am not sure what you mean by hypermobile nerves, but the symptoms you describe are consistent with ulnar neuropathy. This is somewhat similar conceptually to the more commonly known carpal tunnel syndrome. The ulnar nerve supplies innervation to some of the muscles and the skin on the side of the arm closer to the body (the "medial" forearm and hand), including the pinky and ring finger. Ulnar neuropathy is a type of irritation of the ulnar nerve.. Ulnar neuropathy causes numbness, tingling, or pain into the arm and hand on the side of the little finger. This is sometimes called "handlebar palsy", because it frequently happens in bicyclists who sustain repeated shocks and bouncing that can occur while holding the handlebars when riding. Other activities that involve stress on the hands and wrists may also irritate the ulnar nerve and cause ulnar neuropathy.
Another possible cause of your symptoms include a herniated disc affecting a portion of the nerves that eventually form the ulnar nerve (specifically the area involved would be a nerve root, the C8/T1 nerve root). Other areas that could be affected is what is called the brachial plexus, a collection of nerves near the collar bone and armpit that eventually move down the arm to form the nerves that innervate the pinky finger and ring finger etc.
Treatment for ulnar neuropathy depends on the cause, and the extent and severity. If it is due to repetitive injury due to specific activities, these should be stopped. Evaluation by a neurologist would be useful to you: after he/she examines you, he/she may choose to do a study abbreviated EMG/NCS which is able to assess how electricity is conducted along the ulnar nerve and how the muscles respond. If the EMG/NCS shows only mild abnormalities, surgery may not be necessary however if the study shows that the ulnar nerve is showing damage, surgery by a qualified surgeon may be indicated.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.