Well, swimming is going to have to go on the shelf for at least a month or so. I saw an orthopedic PA this morning and he said it's most likely a torn or inflamed labrum. I had no idea what that was until a couple of hours ago. Apparently it's the tissue surrounding the shoulder socket. According to the internets, tears are often caused by repetitive motions or a sudden pull, such as when lifting a heavy object.
Which basically confirms to me that I hurt it when I took that surfing lesson last September. It started hurting the next day. The instructor gave me a GIANT surfboard and I vividly remember several times when my arms were jerked as the waves pulled the surfboard out of my arms. Although I'm heavy, I'm not super tall and I think that board was too much for me to handle. Ever since then I've just been exacerbating the problem when I went to the pool and swam laps.
I have a prescription for an anti-inflammatory and start physical therapy in a couple of weeks. Hopefully I will have improved enough to not reinjure myself when I do the St. John swim at the end of May. Because there's no way I'm skipping that. However, this makes me really glad we decided to do the swim with fins. I definitely know I can swim 1 1/4 miles with fins, even if I don't train between now and then.
My fingers are crossed that we can get this fixed and it won't hamper my swimming long-term.