I've been told babies often start sleeping better during the night around 3 months of age. You are very lucky it is happening to you. I don't believe you should wake a sleeping baby. If they are hungry, they will wake for a feed. If not, enjoy it while you have it.
Your milk will adjust to your baby's needs. It will definitely not dry up. My five month old sleeps through 8 hours without a feed and my milk does not suffer. and if he's going through a growth spurt and wants to feed every two hours during the night, my supply doesn't run out.
If you want to pump you can, even if it is just a little to relieve the breast. Otherwise give your body time and it will adjust to what is hopefully a new routine for you (with extra sleep)
Tans