Implantation bleeding (tmi pic)

My period is usually 26-27 days from the start of my period to the day before my next period. I have been ttc for 4 years with no luck. I have a7 year old, so I know I can have kids. This month, I have yet to stay my period and it has been 31 days since the start of my last period (which is unusual). This morning, I am crampy and my morning pee, when I wiped, it was pinkish brown. I got upset and was leaving the house so I put a tampon in because I thought that was the start of my period. Well, 2 hours later, I pulled out the tampon and there was light brown spotting. 3 hours later, nothing more. Is it to late for this to be implantation bleeding? I took a pregnancy test today and so far it's negative. Is there hope?