13dpo and going crazy

So I've decided my bbt chart is null and void as been doing it all wrong! I've been doing it before bed (granted atleast at same time) but read loads of stuff since that says it can only be accurate at resting rate first thing after sleep- stupid me!

ANYWAY..... I'm now at 13dpo had cramps and sore boobs for 2 weeks, the odd wave of nausea (which could be attributed to anything else!) AF was due 3 days ago and today had the slightest of spotting - pink cm only when wipe and now it's stopped again- could that be implantation? Also tested this morning and got bfn - anythoughts? Xx x