I had my period 3-4 weeks ago, Then I had sex 3 days ago with my boyfriend. Today I started bleeding a little bit, then it stopped then it came heavy & stopped then it got clear and liquidy. What does this mean?

Did you use contraception? If not, you potentially may have experienced implantation bleeding, which occurs when a fertilised egg implants itself in the uterine lining. Many women confuse this with their period, but it also doesn't happen for many women, so don't convince yourself that it is indeed that.

There is no way to know for sure what the bleeding was, as every woman runs on a different menstrual cycle, and not knowing your full situation it is hard to tell. If the bleeding was at all different from your regular period, I would recommend visiting a doctor or taking a home pregnancy test, just to be safe.

It is not possible to know anything at this point, it could be implantation bleeding for pregnancy, the timing is correct. But you will have to wait and see if you miss a period or not.