Strange period, and I\'m not on any birth contorl.

I am married, not on birth control and my husband and I are sexually active. Most of the times we use condoms, but only half way through (we stop and put one on). A couple of times we have tried the 'pull out' method. Anyways. I never have 'regular' periods. Typically, they are about 2-3 weeks apart from each other. I began a period on September 19, 2009 which lasted until September 24, 2009. This period was brown, light and had a little bit of pink to it on day 2. On October 4 and 5, my husband and I had intercourse using the 'pull out' method. Then when I woke up of October 6, I had a milky brown discharge that came onto my panties. The discharge has continued but is extremely, extremely light. (Today is the 7th). What is wrong with me? I am concerned that I am possibly pregnant. (I did take a pregnancy test on September 29 because my period was so strange, but was negative). Another concern is that since my periods are off (and not red) can I even become pregnant? Any response would help. Very curious. (Pap smears are always normal).