Missed cycle in may with a neg preg test and early cycle in june. july's cycle is late according to the new scheduled time. what could be the issue?

Irregular cycle: I will assume you are not taking contraceptive medication. There can be several factors, from physiological (normal) variations, although, if you have been regular is unusual. You need to take in consideration like possible female organs infections, hormonal changes of other origins, etc. I would strongly advice to visit your Obstetrician to get to the end of it. It may be something more.