Take plenty of fluids  fruits and vegetables If constipation is still not relieved add isabgol 2 tsf at bedtime Milk supply is affected by plenty of factors including your mental state your hydration and if your baby is taking any topfeed Keep yourself hydrated with lots of fluids and juices and try to exclusively breastfeed your baby 

if there is constipation there is less amount of water intake in your body that can also affect the low milk supply so hydrate yourself nicely with lot of milk fruits juices soups etc