This may help with your question concerning your IBS.
https://www.healthline.com/health/irritable-bowel-syndrome/ibs-fasting#it-may-help
This too may assist your search.
Can IBS be made worse by allergies? https://www.avogel.co.uk/health/digestive-system/ibs/can-ibs-be-made-worse-by-allergies/
Candida can cause depression if you suffer the symptoms overlong. Many allergies can be helped with a change of diet too. Candida can also be helped with a diet change. Some of those foods that feed candida are processed sugar products and dairy. Dispense with diet sodas, or sodas generally too. Diet soda is horrible for the body.
A friend of mine was a nutritionist. Years ago I gained weight due to depression having lost a family member. I replaced them with eating anything in sight. I looked ridiculous! That's where I got my advice I share from time to time now.
They helped me understand about supplements to get me back on track while eliminating gradually over time foods that were bad for me. Fasting was one method.
A week is a long time to go if you've never fasted. Maybe try to fast for a couple of days and see how you feel.