This is a hard situation to be in, and it certainly isn't helping your IBS. I am guessing you are not paying rent, is that right? Maybe your mom feels that it's unfair for you to live in the house rent free and also without consistent contributions to the household. Even though you do have a job, if you don't contribute any of your earnings to the costs of running the house, then your mom may have a reasonable expectation for you to do something else instead.
Maybe a good resolution would be to sit down with your mom, when she's not angry, and ask her what chores she thinks it would be fair for you to do on a regular basis. Negotiate with her. Come to an agreement that works for both of you, and then stick to it the very best you can. Do things before she asks you to. This is a good way to show appreciation for her allowing you to live there rent free. Not all parents allow this - may parents didn't.
I understand about feeling sick, especially in the mornings. Those are the worst for me too. I wonder if it would help you to get up and move around, and in fact maybe do some chores or other activities in the morning when you're feeling ill. I've done that on a few occasions and it has helped me shift my focus from my symptoms, and in turn helps them pass faster, or at least with less suffering on my part. Too much focus on IBS perpetuates the cycle. I'm working on that aspect as well because it is very difficult not to focus on it when you feel so ill.