Is it possible to become pregnant on your period ? I've heard ys and no

Yes it is possible to conceive when you have your period.

If a woman has a short cycle -- typically 21 days from first day to first day -- then she is actually ovulating on day seven of her cycle (the seventh day from the first day of her period). Because some periods last that long, it is possible that a menses may be just ending when she is ovulating.
Also, some bleeding may not be necessarily a real period. Occasionally, ovulation can cause some spotting, which can be mistaken for a period. A woman may think she is safe just at the most unsafe time.
Bleeding may represent implantation of a fertilized ovum, too.

You're less likely to. But I is definitely possible