Thank you for the question.
Here are some thoughts based on what you are describing:
1. Menopause in the mid-40's is earlier than typical, but not completely abnormal
2. You are still relatively young and not near when other women in your family go through menopause
3. Birth control pills for 15 years does not affect fertility or egg quality - you did not imply this but if you are worried, I just would like to mention this fact
4. Most women have 28 day cycles, and an interval of 25-28 days is completely normal. The most important thing is that they are occurring monthly. This is the best sign that you are cycling normally
5. The 'quality' of eggs is not related to your cycle interval - you are still young and they are likely of high / normal qualty
6. There is a lab called 'AMH' that can be drawn and it is an excellent measure of egg quality
Does this answer your questions?
A slightly shorter cycle interval like you are describing is not, in and of itself, a sign of poor egg quality.
With regard to ovulation: In the first half of your cycle, you recruit 'eggs' / cysts in you ovaries. One of these becomes the dominant cyst and as you approach ovulation (the release of the egg), the cyst gets big quickly and then bursts open releasing the egg. There is commonly a short period of cramping on one side or the other associated with this event. This is all completely normal!
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