Considering your age, you can be having pain due to the erupting wisdom tooth, which might be covered with gums partially. There might be pus build up below that which might be causing pain. Once you had that ulcer, the pus escaped and you felt relief. But this is only a guess work, because I haven't seen your case. You can visit my clinic in sector 40 I'd you want. I'll check and guide you further.

As per your history it looks like a traumatic ulcer which should subside once the irritating factor is removed . In this case it must be the wisdom teeth . I suggest you to extract the wisdom tooth in order to her permanent relief .