Re: First Time Sexual Problem.
Did he came inside you between the two sessions? If yes, it may be the cause. The cement would become a troublemaker for vaginal lubricant function (under condition of your body when having the sex).
In such condition, the natural mucous or woman's lubricant becomes a bit stretch (only he knows), not oily/lubricating anymore. Hence, it may become the grease inside vaginal walls. Beside the next session takes longer time, so frequency of friction becomes more higher.
IME, most of time, my mate would complain about the sharp pain several days after, if I let the ejaculation inside her, and proceed for the next round not for awhile. But it did not always happen. I had analyzed that she won't get the problem, around her fertility period. It makes sense though, because best quality of lubricant were plenty produced at that time. Briefly said, the genital is in full service by accepting any cc of cement that com,es inside, but it won't lose the balance of pH, quality of mucous, or sort of supporting aspects. Btw, she's in on spiral, so I can notice it better without condom. Of course, after having a mutual interview with her, I break my curiosity a bit.
The balloon might be anything. But if it felt great then it's possibly the g-spot or the best eregenous zone. Some woman may have a bigger size g-spot "pimple-shaped" which is sorrounded by another smaller mounts around the zone. I'd been searching in most forums, most of couple who had been together in long time enough of sex, may find it at last. So, it did happen to us, took two years until I knew where exactly her eregenous zone was located, and she confirmed for it.
But, the best thing is to have it checked at gyno for best result. Hopefully, it's not a "strange-unit", hopefully it's just because of friction cause from the sex.