CD 36 brown spotting no period

I've been having brown spotting and AF like cramps for three days but no period. Currently breastfeeding my 18 month old so that may have effected it? I think (but I'm not certain) that I ovulated 9 days ago (had an almost positive opk then it went back to super light). The only other time I've had brown spotting was when I was pregnant last year with the baby I lost. However my hpt was negative tonight but I have a very dark opk. Opinions? Anyone have similar experiences?