what can this be? implantation bleeding or period?

for the last couple days my stomach has been feeling weird.no other symptoms. hubby always pulls out, we have been doing that for so long now, and never felt like this before. we have a 9 yr old son and a 4 yr old daughter. after my daughter been born we been always using the pull out method and nothing happened. on monday the 19th Woke up like around 4am with some cramps and a weird feeling in my stomach went to the bathroom and there was some blood like my period was starting. so i put on a thin pad. well today is the 21st and still have this weird feeling in my stomach and when i go to the bathroom there is some blood and some blood on pad and but not enough to change the pad. what do you think? is it just my period being weird? i usually start light and then start getting heavy but this month it seems different. what do you think?