advice please!

Emma
I'm only 4dpo but today I've had some brown discharge, only  a tiny amount once after I had a wee. I've also had some mild stomach cramps but I've been putting this down to being struck down with a 24hr sickness bug this week. 
When I google (worst thing to do I know!) brown discharge it suggests implantation bleeding.... Could it happen this quickly? Or is there a slight chance I could have conceived last week prior to my 'green days'??
TTC for 10 months now and it's driving me a little crazy!