What would cause my periods to be like this?

I have a normal cycle. 30 days between and my period lasts for 6-7 days, first 4 days bleeding steady and the rest spotting. I usually get cramps the first couple days. Last month I started a week and a half early and it lasted 3 days, extremely light, not steady flow, and no cramping. This month I was a week late with very light unsteady flow the first day with almost nonexistent cramps. and the next two days with spotting. There is a great possibility of being pregnant. I've had many pregnancy symptoms: headaches, nausea, sore swollen breasts, drinking loads of water causing me to urinate frequently. If this isn't decidual bleeding, what else could cause this?