breastfeeding and possibly pregnant

Ok baby is almost 5 months old and we have been trying to get pregnant after 3 months... I have had regular periods since one month post pardon ... it's too soon to test but I'm supper tired and I noticed today my boobs aren't as full as normal...I eat oatmeal each day and drink lots of water... any suggestions to keep milk supply up and what to do to keep it up till 6 months when we plan on weaning off.