Is it possible you've hit it on something and maybe bruised the bone? If you're having trouble actually moving your arm with this pain, that warrants a trip to the doctor and an X-ray to see if there are any chips in the bone.
I have been dealing with elbow/arm pain for several months now as well, and I can only guess it's from all the arm work at AquaFit. My right arm is the worst (even though I broke my left elbow many years ago) - I can't even run my finger lightly down the back of the arm without pain...it's like I'm hypersensitive to any touch.
You could be dealing with any number of issues, (strain, sprain, bursitis, etc.), so ask your doctor about it, just to be safe.
Conditions: Fibromyalgia, Severe Myofascial Pain, Chronic Pelvic Pain (with permanent muscle damage), Femoroacetabular Impingement (CAM and Pincer), Reynauds, IBS, Surgical Adhesions, Ophthalmic Migraines, Severe Hot Flashes (both Surgical Menopause and medication related), plus physically unable to vomit due to the Nissen, and I have extremely tiny veins with a lot of scar tissue...a joy when it comes to having to give blood or get an IV started
Surgeries: Appendix, Uterus, Nissen Fundoplication for GERD, Left Ovary, Gallbladder, Right Ovary, TVT
Medications: Oxycontin, Cesamet, Tramacet, Cymbalta, Flexeril and Clonidine plus Laxaday, Vitamin D and a Multi-Vitamin daily