Any time you have sex there is the risk of pregnancy. If your period is expected to start 30th Jan, it presupposes ovulation on 16th Jan, indicating you were fertile 11th to 16th Jan. However, if you ovulated 5 days earlier, then 6th Jan would be in your fertile time. But that timing for ovulation would bring your period forward 5 days to 25th Jan if pregnancy did not take place. The mention of 3 days after your period ended is not much help without knowing how long your period was.
So if your period started 30th Dec and you expect the next to start 30th Jan you are working on a cycle of 31 days. If your cycle is regularly 31 days (so your following period would be expected 2nd March), then the chances of an early ovulation are low, providing there have not been any significant changes in your system (illness, stress &c).
How irregular. Can you give a range? 28-32 days or something like that. Or is it very irregular?
In that case, it is impossible to predict your fertile days, but the chance of being fertile so soon is very unlikely if your periods are always at least 28 days apart.