I'm not sure if I can relate, but I have type 1 diabetes and celiac disease and am often very sick while at other times I feel completely fine. I've been dealing with diabetes for over 3 years and celiac disease almost 2 years, and I still haven't figured it all out either.
First of all, never ever take advice from healthy people. Nobody who also has a chronic illness can tell you how to deal with your problems. Their advice usually doesn't help and you will only feel more sick, tired and further away from your goals.
A big danger is that you pretend to always feel fine and don't show your limitations. People think you're strong and hardworking, but often have no idea how sick you really are. You will not get the support you need and will often feel lonely. This is what I've done and it worked out for a while, but it's just a matter of time until you crash.
You cannot push through the limitations that your body has imposed on you. It might work at first but you will crash. You are limited in what you can do. Your disease is often unpredictable and on one day you'll be able to do whatever you want and other days you can't even get out of bed. The entire world is created and ran by healthy people. If your friend has a party, he can't suddenly move it because you're sick. Work, school and everything else often aren't very flexible in that regard either. You can usually get extra time for tests and things like that, but it's almost never enough.
If you're like me, you'll try to stay strong and work even harder. You want to reach your goal and not disappoint those around you, so you pull yourself together and keep going, even if you really can't. The result is that your problems, pain and tiredness only get worse. You'll have to stop.
It's very confronting, as you've gone over your limits and have more pain, you're also sad that you couldn't reach your goal, or not in the way you wanted to. It's very frustrating and your self-esteem takes a big hit. Some people decide to often never do anything anymore, because then atleast you can't fail and you don't get sicker. That doesn't work either. You have to set goals to be happy.
There's also some more general advice I can give people with chronic illnesses. I've formatted them into "the golden rules"
Before you set a goal you must know what you can and cannot do. You must realistically look at your health and know what you can and cannot do. Don't forget to trust yourself and your possibilities. There are always people who will assume you can't do anything because of your illnesses, but don't let them affect you. Also beware of being too optimistic of your abilities.
Do what you love to do. Don't be afraid to reach for the stars, but keep rule 1 in mind. Some people want to "just be able to work", but remember the kind of desire that's beneath your goal. If you want to be independent and make your own money, then you must keep that in mind, as it will help you reach what you want.
"It won't work out", "I'm too sick for this". These are things I often find myself thinking if I feel particularly bad. Don't make plans based on these thoughts. I'd advise people to try to put them out of their mind, but I know that's impossible. Just know that you will feel better later.
You cannot adhere to deadlines, ever. Chronic illnesses are often extremely unpredictable and you never know how you will feel. You can't set goals like "I will do 50 pushups every day" because you physically won't be able to do that. You might be able to do 100 some days, but not even 15 on others.
This is also good advice for people who don't have chronic illnesses, but don't be afraid to reward yourself. Even if you fuck up. If you want to run 10 miles but it's raining and you only ran 5, it's completely fine. Get yourself a pie (or something else if you're gluten intolerant like me) and celebrate.
People with chronic illnesses have to climb longer and further to reach their goals, but the view will only be better. If you can overcome your illnesses, you've already achieved more than 90% of all people in the world.