I need some help!

4 negative pregnancy tests, I'm now 8 days late and still nothing,

I'm experiencing;

mild cramping (like period pains),

Sore and tender breasts,

More frequent toilet trips (urine)

I even had heart burn for the first time ever last night.

I had unprotected sex with my boyfriend right after having my coil out and I've been on no birth control since. He's being "pulling out" but I know this doesn't always work.

What do I do? Could I be pregnant?