That is impossible to say, since you are clearly not on a 30 day cycle.
But in between the periods would be the most optimal time.
And you need a work up from a fertility specialist.
With this degree of being off a regular cycle, hormonal problems might be getting in the way, and you should have a sex hormone panel, thyroid studies, and adrenal studies.
If you take your temperature daily at the same time, in theory a light rise in your baseline temperature will be ovulation.
Also remember that a home pregnancy test is going to take 2 to 4 weeks to show positive.
However, a period every two weeks might indicate a problem, or not.
I would see a fertility specialist, and this is usually an endocrinologist.
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