Make sure you are drinking 1 gallon per day of water. Also my dd is 12 months also & my period returned when dd was 8-9 months I think. I know that these babies have 100 things to look at rather than nurse lol but they are very efficient at this age. Dd doesn't really eat that many solids either and is night weaned but will nurse 5-7 times per day for anywhere from 2-10 mins each time.
Is your son gain well - like is he under weight?