Back,
Man that does add to the stress. And I bet she has forgotten to some degree about you. When I got married I explained my theory about how it was all supposed to work. The kids came first above everything else. then my spouse came next. Then I did.
I couldn't apply that in my first marriage. She just was concerned about herself. My second wife is very different. She and I both work hard to place each other in front of the other. Its not always easy to do. But it is very rewarding when you have done it and the other person realizes that you did. Very powerful.
I don't doubt your lady has placed your son above your problems. She had a kid. Your married to her and I am sure she loves you and all that mushy stuff... but a kid? Especially a sick kid? WOW! that's a person she raised inside her. Most moms will always put the kids above everything else. I think my first wife was an exception to the rule.
Maybe a new approach is needed? Thank her for what she has done. Seriously. Tell her you know its been hard. Be honest. Tell her your feelings about how you feel like your being ignored. But before you do, I would have a plan in place. If it were me, I would tell her how you plan to remove some form of stress she is dealing with concerning your son. Maybe offering to take him to a medical appointment so she can stay home and catch a nap or a hot bubble bath. Something to show her you care about her. Not just words, deeds. Action before words. Don't just do it once, do it a lot.
Making changes yourself should open her eyes and help her want to do things differently for you. It will show you just what your relationship is all about in a short time. If she reacts and replicates your actions, you have a keeper.
Good luck!