I took half the dose of a morning after pill weeks ago and haven't started my period?

I had unprotected about 16 days ago. I took the morning after pill within the 72 hour time frame but only took half the dosage. Does half the dosage still work some? A few days later I had a little bleeding but it was old, brown blood- never bright red like my normal period. I haven't had any bleeding since then. Could that have been my period or a side effect of the pill? I have also developed BV since then. Is this normal? I'm worried because I don't know what's going on.