small blisters

I am a 43 year old female in generally good health.  Take Toprol XL 25 mg daily for heart palpitations, but otherwise good.  I recently had a project that required me to be outside for 12 - 13 hours a day for 8 days.  I thought this would be a great time to get a little sun on my arms so I wore short sleeves.  I did get burnt by about the second day, but I was not in any pain, just red.  By the fourth day I started noticing blisters on my arms and thought that it was from the sun, but then they just kept appearing.  I then thought that because I was exposed to wood being chipped (along with poison ivy) that maybe I had an allergic reaction.  Then I thought it may have been photosensitivity due to the Toprol (and I was also taking Acylovir for the first few days of sun exposure).  The last several days of the project I wore long sleeves and thought this would help as the blisters started going away.  I have now been out of the daily sun for five days and I am still seeing small blisters appear.  They do not itch, but are red, small, and water filled.  They can appear anywhere, even in clothed areas.  Did not have this problem before this project and generally work at a desk with very little sun exposure during the day. Anyone got any thoughts???