Hi I Haven't Had A Period In 2 Months. But

Hi i haven't had a period in 2 months. But did have dark stringy like substance that lasted for a week, this happened a week before my period was due in September. About two weeks after that i had it again but for two days. Could i be pregnant or do you think it's something more sinister? iv felt a little bit nauseous after eating too but not all the time. Been a little bit stressed about things too, but this has never happened to me before.