Mum2Romone - It really could be anything. Could be O, or af, or just random backpain. Your cycle could be messed up for a while after a mc. When it comes to OPK's, usually they have a guide with them that explains when to start testing. You're meant to test so many days after af, according to your average cycle length. If you were to start testing now you could go through an awful lot of them, but if they were cheapies and you have a lot, there's no harm in starting now if you want to. Sorry, that was pretty vague but there really is no rulebook to how these things work sadly.