Pains and Brown Discharge

Hi. I was wondering if anyone had any advice on the following. Hopefully I wont confuse you too much with all the details. Me and my partner had a son in June of this year and after being on the pill we decided we would like our 2 children to be close in age so I came straight off it again in September after being on it for only a month. I had my "pill" period on time around 29 September. After approx 6 weeks on 12 November I had a 3 day period which seemed shortly than usual. A week after this I got a brown discharge which over a course of about 3 days seemed to have got a bit darker. I understand this could be for a number of reasons ie old blood, being the pill etc etc. I did a couple of pregnancy tests before I started the lighter period before 12 November and it was negative. I am not sure if to do another one again as if the lighter period is indeed a proper period then now will be too early? Also last night I got period type pains but obviously I am not due on for another couple of weeks so am confused as to what this is. Has anyone else experienced this brown blood following a lighter period? Any advice would be greatly appreciated. Thanks.