You can try taking a multivitamin if you don't already. I find when I have irregularities in my cycle (usually due to stress) that taking vitamins helps a ton. I use the one linked below - it contains some dong quai and chaste berry which help with regulating your menstrual cycle. I take one a day (recommended is 2).
I would not get overly concerned with infertility, it's most likely just that your body has experienced something out of the ordinary and is reacting accordingly - it's pretty normal. I am not a doctor by any means and haven't experienced menstrual changes from the vaccine so far, this is just what has worked for me in the past with some occasional irregular cycles. I hope we start to hear more reporting on this. I think it's probably a fairly normal reaction, but it's clear they haven't studied it enough to report on it. No one wants to talk about periods.