Hello, I had a similar difficult time with my son; tt can be really tricky not least that it causes a high palate to be formed within the womb which adds to latch issues.
I did have over supply too due to bad advice and too much expressing.
I think the first thing is to get some really good advice on latching; if you can get a really experienced peer supporter or lactation consultant to observe you this will help.
I think block feeding is a tricky one as it's trying to find the balance between calming the supply but not cutting it off as baby needs it.
Read this and see if it helps - I did try block feeding and it did help and we got yellow poos after about 5 days I think but I do wonder if there were other things I missed too.
http://www.nancymohrbacher.com/articles/2014/5/21/green-poop-when-should-you-worry.html
Google dr jack Newman on YouTube and compression feeding too. He also has some things to say about oversupply and green poo too but it can get a bit complicated.
Check your latch is really good - pull baby's bum into your tummy and press gently / support between their shoulder blades so their head is free to move.
I found feeding lying down very helpful as my son struggled with the let down. Make sure their chin is touching your breast if you do this; I'd also recommend compression feeding if baby nods off to make sure the breast is being drained.
There's no magical switch over to hind milk but it is fattier near the end hence Newman's approach. Some don't believe in block feeding for this reason. (Sorry I know it's confusing!)
Infacol is useless but colief might help a bit (expensive but v useful) as it helps them process the lactose. It's just lactase. Bit faffy but you can express onto a spoon and syringe it in.
I really did find a small amount of baby gavisgon helpful; didn't need all the time and I just mixed a small amount in.
I do remember having to keep my son upright all night which was exhausting.
a really good firm circular clockwise massage on his tummy while he stretched back over my thighs helped shift tummy wind. But it's trial and error.
Lastly I'd check there isn't a uti going on as actually I found my son did have one which made him sicker.
I was advised to try cutting out milk myself too - you could give it a go; some friends have found it really helps.
And congratulations!