Usually my period lasts 5-6 days and is pretty heavy and all red except for the last day. This last period however was much more brown, lighter, but had one or two days of full red bleeding, and lasted a total of 3-4 days. I didn't get the usual cramps I get and its consistently heavy and long. I am sexually active and use only condoms as contraceptives, and I have ready many things online saying there's a possible chance it's implantation bleeding, and I'm worried that it's that. I'm not sure why my hormones would change that much, I haven't taken birth control or had any drastic changes in lifestyle. What are the chances its pregnancy and should I be worried?