Brown discharge instead of period.

So I'm on birth control, and today is supposed to be my second period day. I haven't had a period in a few months, because sometimes when taking my birth control, I just don't bleed. But today I've had creamy, light, sometimes a little darker, brown discharge. Everything I've read is either "implantation bleeding!" Or "just old blood." But I haven't had a period in a while and j have regular discharge throughout the month, so could it be old blood....?