Could i possibly pregnant after having unprotected sex then cycle comes on rite after that with a much more heavier and painful cycle?

Check preg test: First step is to check a pregnancy test. Over-the-counter pregnancy tests are cheap and reliable. If the test is positive you will need to seek prenatal care. If the pregnancy test is negative then wait to see if your cycle comes soon and if not schedule a visit with an obgyn.

Highly unlikely: As long as you get a period after unprotected sex, that's usually good evidence that you're not pregnant.

Very doubtful: if you had a period since last sexual intercourse. When ever in doubt you can take a home pregnancy test.