You have information overload because it sounds like basically everything is wrong. The malaise over your relationship is physical, social, psychological, and spiritual. Anyone would feel overwhelmed in your shoes.
.
You're right to ask for advice. Reflect on the advice you've been given, pick 1-3 things to try to implement. Remember that online advice is just that: advice from strangers who don't know you and whom you don't know. Take as much salt as you need to, pray for the prudence to understand what applies and what doesn't.
.
Let me offer additional (male) perspective on a few things:
.
1) Your husband said he would be fine if your relationship didn't generate children, and he probably meant it when he said it, but at a certain point he's not going to be fine with it. This doesn't mean he doesn't love you. But I can pretty much guarantee you that after four years he would prefer your marriage to result in children. When you set out to do the trad Catholic thing-- you're ready to sacrifice and do what it takes (and it takes a lot) to raise a family on one income and provide, but there's no children, a kind of despair can set in. Because your family doesn't actually look any different than a typical DINK's family. Except unlike a DINK you're not enjoying anything the world has to offer. This is part of his and your problem. Explore fertility treatments/supplements (not immorally, of course). It will reintroduce purpose to your marriage.
.
2) It's time to try something new to give your husband purpose. If for four years (perhaps longer, depending on how long you two courted) you've been chasing different diets and exploring a bunch of fringe health solutions-- few of which have made a substantial difference-- go off script. Build a Lego set together. Get some exotic plants or a terrarium for the apartment. Play video games together. Buy some adult coloring books. Get him a model train set. Buy him a fishing pole. Like literally anything that constitutes a hobby and might shake him out of his rut, as well as the rut you two share together. It doesn't sound like it can get worse and it doesn't sound like what you've done so far has made that much difference. It's likely that a hobby won't solve all your problems, but the old saying is that a change is as good as a rest, and it might help jump start something.
.
3) It isn't normal that a ~20 something y.o. man with a new wife and no children doesn't have energy or motivation for sex. I know you're not looking for diet/health advice, but if you are doing everything you can to make him interested, there's something seriously wrong with him. Does he have pornography habits? You don't need to answer that. And if you don't suspect it, you don't need to start suspecting it. Men aren't very good at hiding it even when they try. If you already suspected it, and if there's something to it, absolutely nothing will improve until that problem is excised like the cancer it is.
.
4) Explore the tick-borne illness angle.