I would not assume it is an std, I don't think symptoms usually appear this fast. I have seen something like you are describing and in that case it was a tear in the skin of the vulva. It was very painful and also very itchy.
They don't look like typical cuts because they are in an area that stays moist. If you have ever looked at a cut inside the mouth (cheek, gums, inside of the lip) it would look similar. (I hope I run across a good photo someday, that would be immensely useful.) It was very painful and also very itchy.
How has your sex been? Has it been pretty rough? That is not the only cause of this but it is one of the common cause. Other causes include being to vigorous or using a rough surface while cleaning the area in the shower or bath. That happened to my wife and it did look like what you are describing.
I certainly can't replace a doctor and must always recommend seeing your doctor about it. But if it is the same there are some things you can do. The first thing is keep an eye on it and go to the doctor at the first sign of infection. The second is don't make it worse if you can help it. If sex bothers it then it might be best to abstain from penetrative sex. Oral sex is always good as long as he is giving as good as he is getting, anal sex is also an option, and you can always let hands help each other out. And if you just can't do without, just be careful and take slow.
If it itches do not scratch it! Even if it is intolerable because you will reopen the injury every time which keeps you in a cycle of pain and itching that may lead to a serious infection. The good news is the treatment I am going to suggest should deal with itching as well as protecting the injury.
The nurse suggested using a thick lotion like A&D ointment, desitin, bag balm, eucrin, or even vaseline if we had nothing else. These lotions are often used to treat diaper rash, so this sounds rather weird but it did work very well. We chose the lotion Eucerin. You need it to be thick and difficult to spread so it forms a good soft barrier, so the original formula is what we used. It is thick and comes kinda like a pot - you reach in with your hand and scoop it out. Apply it on the affected area but do not rub it in all the way - you want it to stay put - and reapply as necessary. It forms a water and air proof barrier that also cushions the injury. This stopped the itching and the pain which allowed it to heal quickly in a couple of days.
If this is what it is, you are not alone. Others on this site have had the same problem, we originally learned about this while search the women's issues part of this site. Many women get these, often from rough sex, but frequency varies. Some rarely or never get it and some have it happen frequently and they didn't even do anything to cause it. Hopefully you are not that susceptible.
Again, obviously I am not a doctor so don't take what said here as the answer. What I suggested might help, but the key question is, is that really what is happening? Going to the doctor is always a good idea if you have insurance or can afford it. You will need to evaluate your situation and decide what to do.
I just remembered another treatment option the doctor suggested, a sitz bath using epsom salts or just soak in the salt solution while in the tub. This is only short term relief but it may be enough for you.
Please let me know if I can be of any assistance.
- Miles, HypnoMorph