>>21670826 (OP)
Rather than restrictions, I would focus on adding things into your diet that support the immune system. Vitamins A, C, D and Zinc in your diet are obviously important, but you could also consider foods with antimicrobial properties and foods that improve digestion.
Antimicrobial foods:
Garlic
Ginger
Turmeric
Cinnamon
Cloves
Cumin
Allspice
Nutmeg
Cilantro
Thyme
Basil
Oregano
Rosemary
Fenugreek
Tarragon
Bay leaf
Anti-inflammatory foods:
Green tea
Turmeric
Licorice root
Foods that improve digestion:
Probiotics (kefir, yogurt, kimchi etc)
Peppermint tea
Pineapple
Papaya
Mango
Figs
Kiwi fruit
Ginger
Dandelion
Turmeric
Fennel
Teas in general are very good for immune support. Green tea, earl grey tea, and all kinds of herbal teas from the list above. Masala chai contains multiple of the spices in this list, and is very tasty.
Basically to assist immunity you want to keep digestion moving as efficiently as possible. Most diseases are connected to poor gut health. You gotta poop more often OP. Aim for twice a day!