Re: Is this oversupply??
Hi mama, and congratulations on your new son and 18 days of breastfeeding! You have made it past what is usually the hardest part.
Everything you write here sounds absolutely normal. Lucky you on the 4-5 hour stretch at night - and remember it'll change. Since it sounds like he's gaining well, this is probably not a cause for concern. You mention frequent poops - that's normal - but also make sure he's having at least 6-8 wet diapers a day. If he is, he's doing fine.
Feeding for long stretches, especially cluster feeding in the evenings, is totally normal at htis age; just grab a book or a computer, water, and a snack and settle in for those long nursing sessions. It doesn't mean he's not satisfied - it's just how babies eat, and it's how he is telling your body how much milk to make.
Remember that your supply won't regulate really for a couple more weeks, at which point your strong letdown might resolve itself. It sounds like you're managing that just fine, though. Mamas who have oversupply are often noticing that their babies choke, gulp, and pop off the breast a lot - if yours isn't doing this, then don't worry about it. Just keep feeding at earliest cue and enjoy those precious newborn days!!
Nursing, pumping, cloth-diapering, babywearing, working professor mama with the awesomest SAHD ever.