Hello,
These blisters can be due to friction blisters or herpes sores. When signs of occur, they typically appear as one or more blisters on or around the genitals or rectum. The blisters break, leaving tender ulcers (sores) that may take two to four weeks to heal the first time they occur. Typically, another outbreak can appear weeks or months after the first, but it almost always is less severe and shorter than the first outbreak.
I suggest you to get a blood test for herpes done to completely rule out herpes.
I hope it helps. Take care and regards.
do you still have these blisters? if so 5 years is a long time to have anything without geting it seen to. you really need to c ur GP and find out whats goin on and get the proper treatment.