Period cycle

How is it possible to bleed a little or a lot and still be preagnant

Yes it is.

When I was pregnant with my son I had implantation bleeding which lasted for 3 days.
I also have 3 period - like bleedings for 3 months into my pregnancy that were very similar to a period and lasted for 4 days each.

My sister didn't know she was pregnant because she had a period the first 5 months of her pregnancy, so it's more than possible.

The body has to do some adjustments when you are pregnant and that includes your period. It is perfectly normal but if it exceeds five months and the periods are heavy, then its something to call the doctor about.