Irregular cycles

Hello everyone, so I am 19 years old and for the past three years I have had very regular cycles, exactly 28 days, ovulation on day 14 and my period last about 6 days. However, since April it had gradually gotten shorter. I had a 27 day cycle in April. 26 days cycle in May. 23 day cycle in June and 24 day cycle in July. I am very confused as to when I will be ovulating and when My period is now due. I’m expecting it to come now early at 23 days but I hadn’t come yet which is worrying me because my boyfriend and I are sexually active.

Does anyone know how periods become irregular and why? And also when roughly I’d be ovulating