What is an option to get the same results without the gut issues

I am over 40 and started the lowest dose of extended release Concerta. Very happy with the improvements in my life. But, I already had lifelong insomnia. I started taking melatonin to try and stop taking Benadryl. I love the melatonin and take less Benadryl. I can’t digest anything and have gotten very food sensitive. No appetite. Awful Morning nausea. Can’t have anything with legumes: soy, peanuts, chocolate, red meat. Is the melatonin and concerta combo messing up my gut production of serotonin? I have lost weight I needed to lose but the process is miserable. The concerta has improved my emotional control, and my ability to function in life and at work is incredible, but I don’t enjoy food at all. Couple bites, done eating. Losing about a pound every 10 days. Lost two pant sizes, for example. Good results, but what can I do to fix the miserable gut?