implantation bleeding or period?

soo always my periods have been pretty regular. maybe a day late or always on time. but this month was a little strange for me. I started my cycle for this month on 2/15. but for the first time I spotted the night before so I wore a liner and woke up the next day with nothing until maybe 10am on the 15 . I'm usually a medium bleeder sometimes I can be heavy just depends. but this time it I was light red and I say in between light and medium bleeding. this lasted until the 16th, day 2. CD 3 was very light 1 tampon lasted all day basically. not normal and I thought maybe it will flow at night . so here it is day 4 no blood all day what so ever . light cramps every now and then and I've been feeling very nauseous lately. I have no Idea what's going on someone help