af happened :/ so sick of this

Well after ms really thinking this month would be the one I awoke to find af has visited :( so fed up of this crap after 2 years of ttc should I just throw the towel in? also I thought I'd look at my bbt I always temp at same time every day and Ive been using opks but my chart just doesn't look right this month :( I would like someone who knows a lot about bbts to take a look and tell me what they think has happened :(