I agree...it is possible, but very unlikely.
Hi!
Technically, since women's cycles can be erratic, you CAN get pregnant from intercourse during your period. Even if you have not ovulated yet, sperm can live for a few days, so if you ovulated on, say, day 7 or 8 there's still a slight chance of pregnancy occurring.
But that doesn't mean it's anywhere near likely. If your cycles are regular and 28-30 days, you probably ovulate around day 14/15.
So, although technically it's possible, you are very unlikely to become pregnant from intercourse on day 4.
Try not to worry - and maybe switch condom brands.!
Best wishes,
~Wendy