What Causes Delay In Periods,nausea And Vomiting?

I think i may be pregnant. i was 12 days late. before i got my period 4 days ago i would feel nausea and i threw up twice. now 4 days after my period i still feel sick to my stomace. i feel like someone is poking my belly button. the most weird thing is. i was 12 days late and the thing that brought my period was walking. i walked like 15 miles. and when i got home my period was supper supper light. and it was light for 4 days. then when i ended my period i went walking again for 15 miles. when i got home i was bleeding again. but light and only for 1 day. whats wrong with me?