Brown discharge, sign of pregnancy?

OK...i have a 21 month old son. Me and my husband have been trying to have another for about 10 months now, with no luck. BUT my periods since i have had my son have been so outta whack. For instance, being late by 3 weeks at a time, then 1 month not have it at all, so it makes it hard to plan for pregnancy when your menstrual cycle is so crazy. My last period started on the 31st of may and now its the 27th of June. I had brown discharge/spotting last night, i thought i was starting my period on time for once,,,but there's nothing today?? Could i be pregnant?? Should i even bother buying a test yet?? Im sick of the disappointment in the negative!...:)..i was thinking it could be implantation bleeding...maybe its just wishful thinking...whats your thoughts?