Logically, menstruation and pregnancy are not possible at same time. Both these conditions negate each other. Some ladies can get implantation bleeding 7-10 days after conception or one weak before expected date of periods. This bleeding is in the form of drops and last for not more than one day. Normally, periods can come after 26-32 days gap. Periods after 32 days and below 21 days are abnormalities and requires treatment after diagnosis from doctor. In my opinion, your early periods are not due to pregnancy but you can satisfy yourself by getting pregnancy test.
Yes it can be. If it is short and is a brownish or pinkish color that could be implantation bleeding.