Ovulate every cycle but not “every month” ??

Probably a dumb question but I wondered if this was normal. Some times I ovulate in the same month af finishes but sometimes my ovulation falls into the next month. Like this for example, I ovulated on 31st of March. But this cycle my ovulation will miss April and fall into may. I use opks and had ovulation confirmed with blood test last cycle so I know my ovulation was definitely March 31st. Is this okay? Is it just because I have longer cycles? I thought you was supposed to ovulate every month? I feel really dumb posting this but I’m a little bit confused