PS. I have pics on my profile
That description fits herpes. A blister that can have a depressed center and clear liquid inside. The first (and luckily so far, the only) outbreak i had started with a single blister that ulcerated, stayed for a week, healed and then the real outbreak started of 3 weeks of constant blisters (smaller than the initial one) appearing, breaking, healing, appearing, etc.
It takes 12 to 16 weeks for the antibodies to show up in the blood, so false negatives for the first outbreak are quite common.
If you did the HSV-2 text early when the blister appeared, you might want to repeat it.
Also acyclovir (i used valacyclovir that is even more effective) did very little for me for me during the outbreak.