5 day old tabby. Constipated? sticky poop? or just not ready?

No one here is going to make negative comments on anything Heather, as this is the fluffiest place on the internet! Welcome to TDK! I had a response typed out on my laptop, when the whole thing disappeared. 🙁
I don’t have any experience using the powdered goat’s milk, so can’t comment on the water/powder ratio. I have used the canned condensed goat’s milk and that ratio to water is 1 to 1. It is awesome and doesn’t cause constipation or diarrhea in hand reared kittens that I have used it on. It sounds like the protrusion in my experience, is that the kitten has poop. It is probably hard at that spot, and have done what you have using the thermometer to get things stimulated. Yes, keep trying as it takes patience, patience and more patience sometimes with some kittens! Try putting a few drops of olive oil in the milk to lubricate inside. I think once you get the kitten started going, you will keep having success.
I am going to post some links for you that are full of info. I know you have hand reared before, as have I, but I have found having these links to refer to gives me confidence that I’m doing the right thing. I will also post a link on the triangle method, it’s actually a video and you might find it helpful also.
http://messybeast.com/handrear.htm
http://www.safehavenforcats.com/newborn.htm

Helping a kitten to eliminate

Please come back and let us know how your kitten is doing!

http://www.felineconstipation.org/acutetreatment.html
I also wanted to give you this link, in case you think you may need it.
I didn’t address your question about ‘sticky poop’. I don’t really know what that means, but any poop at this point would be good. It can’t always be perfect, but normal poop in a hand reared kitten is usually light yellow (mustard colored) with toothpaste consistency. It usually turns a little darker once it has been exposed to air. I don’t think you need panic, you have had him 6 days and he has had one good poop. Just keep working at it, you will finally see success.
And also this link we TDKers use often —

Chaos’ Guide to Constipation

Heather, raising kittens is so much guess work anyway, but I think you are doing a fine job. I don’t worry about weighing, I never did. I fed the kitten, cleaned it, kept it warm, loved it. Weighing is just another thing for me to worry about that I can’t change anyway. I don’t think it sounds like he is sick, and he’s not lethargic. If he should get sluggish and lethargic, and not want to eat, rub some honey or karo syrup on his gums to perk him up so that you can get food in him. But he doesn’t sound like that to me.

Here’s a chart with the minimum weight for each stage:

At age 1 week weight should be approx. 4 ounces/170 g.
At age 2 weeks, weight should be approx. 7 ounces/198 g.
At age 3 weeks, weight should be approx. 10 ounces/283 g.
At age 4 weeks weight should be approx. 13 ounces/368 g.
At age 5 weeks, weight should be approximately 1 pound/453 g.
By the end of the 8th week, kittens should weigh approximately 2 pounds/907 g.

I don’t know for sure obviously, but probably the low blood sugar thing. Tiny kittens like this live from feeding to feeding. This is my explanation anyway– 😉 and their blood sugar drops. That’s why I mentioned keeping honey or karo syrup on hand to rub on his gums to bring the sugar level up and fast. Then feed him once he perks up. Did you feel the heating pad and was it too hot? He should have been able to crawl off of it to get to a cooler spot I would think. Make sure you wrap a heating pad in a towel or some other cloth to not have direct contact with the pad itself. Make sure you check out the links I posted (if you haven’t) because they are loaded with information with people who have hand reared kittens. Keep on with the good work. I know you are exhausted, this kitten raising is not for the weak! Please keep us posted too!