I would love to have baby #2 but he doesn't

I have been with my daughters father for 5 years we have been friends since we were 15 and we are 23 now we have a beautiful smart 2 year old girl who is fully potty trained since she was 18 months we have major problems in our relationship but we have been working on it and now I want baby number 2 because my baby girl is lonely we had sex september 27th and he got a little inside me 4 days later I spotted what does that mean?