Yes, pregnancy is possible. Last November I had the exact same thing, pinkish brownish spotting when I wiped after going to the bathroom and some mild cramps, but no full visit from AF, although I was sure it was coming. On 5 days late I took a test and was pregnant. Saddly I lost the baby at 10 weeks.
Now here I am again, in a similar situation, of 4 days late, but since my misscarriage I have no longer had PMS symptoms that usually help me understand whats going on with my body. I no longer get sore breasts, cramps, ect. I have taken 4 home pregnancy tests from early-pregnancy-test.com and all have come back negative, yet still no period. Last November I used Clear Blue Easy from the drug store and immediately had a positive result. I wonder if my negative result is due to the cheap online brand, maybe I don't have enough of the pregnancy hormone to read, or simply I am not pregnant and just late. No pregnancy is like the other, so it is hard to tell for certain.
Regardless, if your period does not fully come in a few more days, take another test, and regardless if it is negative or positive, go see your doctor, especially if the spotting continues.
Good luck!