breakthrough bleeding?

i've been on the pill for 5 years now and i ALWAYS have regular periods. i've been kind of slipping with my pill lately and i went on a 2 day vacation recently and forgot my pills at home.. so, i went 2 days without taking the pill. the first pill i missed, i noticed some bleeding after sex. the next day, nothing. i came home and took my pill immediately and the next day out of nowhere i got a period flow. it's more like heavy breakthrough bleeding.. it's brown and i'm getting a little bit of cramping and i'm very nauseous. could i be pregnant?? or is it most likely breakthrough bleeding??

the only reason i think it might not be breakthrough bleeding is because usually when i'm done with my pack and i'm on my '' sugar pills '' ( which i never take ), my period never comes on after two missed pills. it usually takes about 4 days of not taking the pill before my period will come on.

xoxo