Help! Missed period.

I have fairly regular cycles: but since I had sex with my ex on may, my cycles started to chance. My periods on may was kinda normal, period on june was two weeks late with one week spotting before my full period and on august, I got no period at all. Its september now and I am starting to get really worried. Im not pregnant because I havent had sex since may and had two periods since then..and as for stress, I have pretty high anxiety in general, not only for these months and I mentioned I have pretty regular cycles. So what is wrong..my periods keep on getting later ...im 23 btw. Anyone else face these kind of issue?