TMI - Looking for Answers...

So I've already called my doctor on this and they told me to test today and in a week if it comes out negative... TTC for 7months now, AF was on time but only lasted 2 days, then this past Saturday i bleed super light colored or brown and only when I wipe. I've worn a panty liner and nothing ever on it, it's now been 4 days of this. Called the doc they said to test and if negative test next week, receptionist didn't seem conerned. Any ideas? Ive never had Implantation bleeding with my first so I'm not sure how long it's suppose to last and I'm trying hard to stay away from Google. And we havent had sex in 5 days. Agggh I'm just so frustrated/lost at this point!