I just saw the other post about RI. With everything you said there I say a vet trip is on order. It sounds like the RI is pretty far along and direct true medication will be your snakes best option.

With a RI you usually want to boost the temp a bit so 75 is not good in your snakes current condition. The uth is not going to help your ambient temps but it is very much needed if it is all you have bu it must be on a tstat.

Do you have a heat lamp or something that can work as a heat lamp? You can very effectively heat a tub with a lamp and after reading your RI post I will say it is most certainly needed.