My LMP was feb.15, and yesterday I noticed some brown/pinkish discharge. Normal since then. Could that be anything other than implantation bleeding?

Possibly. Usually implantation bleeding occurs about a week after ovulation, and assuming a 28 day cycle with ovulation at day 14 the timing is right. It is possible if you have a longer cycle the bleeding can be due to ovulation. Wait a week and do a home urine test for pregnancy. If + schedule your first OB visit.
Possibly. This would be about the right time for implantation to be occurring, so yes it could be from implantation. However, it also could be due to ovulation, which can sometimes result in light spotting. Could also be an episode of breakthrough bleeding for no overt reason. Could be caused by an infection of some sort, yeast or bacterial. Could be due to recent intercourse, if that is the case.