@engrav, a big thumbs up on stopping nicotine caffeine and alcohol! It just so happens all three negatively impact thiamine which might have become deficient leading to some of the symptoms your experiencing. Magnesium is needed to activate thiamine and as the krispin link shows nicotine caffeine and alcohol cause loss of magnesium! Review this information and consult with your health care professional before using any supplement.
https://www.objectivenutrients.com/insights/when-sibo-ibs-constipation-are-unrecognized/
https://www.eonutrition.co.uk/post/thiamine-deficiency-a-major-cause-of-sibo
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8533683/
http://stuttersense.blogspot.com/2014/08/these-factors-reduce-your-thiamine.html
https://www.krispin.com/magnes.html