Honestly, and I wish I had a better answer for you, it could be any of those.
It's not likely to be heat just on the vagina, but it could be shaving, herpes, an allergic reaction to something - it's a long list of possibilities.
If you've had them for a few days or less, and they look like they are fluid-filled, get to a doctor as soon as possible - like today, if possible, and get them cultured with a type specific culture or PCR swab. Any doctor can do this, including an Urgent Care.
It's important to do the type specific testing because transmission of each type is really different.
The longer you wait, the harder it is to diagnose.
Let me know what happens.