It is unlikely that you ovulate on a regular schedule since your cycles are irregular. However, you may still ovulate within the average time frame in each cycle that you do have. It's uncommon, but you can also ovulate without having a period. Only way to know for certain when you might ovulate would be through medical assistance.
Certainly, since you do have some periods, ovulation is possibly occurring at some time as well, so pregnancy can be possible. Plenty of women with irregular cycles become pregnant. It just may take longer than usual.
You would most likely still have a slim chance of ovulating right before a period starts, just like anyone else. Possible, but not likely.
You could always wait a couple of weeks or so and try a pregnancy test.
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