Help.. Brown 'spotting' and tmi description

Before I rush out and waste my money on a hpk.. I think I've been logging my AF fairly accurately. Glow said AF was due yesterday but that would've been 30 days. I average around 29 days so expected AF already. I never get bad period pain but often I get a bit achey and I always get quite tender boobs around 6 days before. Not had either of these things this month. Because I haven't wanted to get my hopes up (been ttc 16 months) I touched round my cervix and have reeaally faint brown looking discharge/'spotting'. Anyone experienced this and been pregnant? 2 days ago I was hopeful, now more so but don't want to get my hopes up too much or waste any more money on opks! 31 day cycle has not happened since I came off the pill. X