I'm going to go against the grain here (boom boom!) and mention that there are a great number of people with autism, and parents of children with autism, that report stomach issues, particularly around wheat products or dairy products.
There is no need to eat specific GF products- as another poster pointed out, many of the foods are very high in sugar, and really not a sound nutritional option. However, it is certainly possible to alter your diet to align with a more Eastern or Mediterranean diet, with a lower intake of bread, cutting cakes and biscuits, and increasing vegetables and fruits.
Many, many dishes are accompanied by rice (brown is healthier, but takes longer to cook), or potatoes, or other grains such as buckwheat (which is not wheat!), quinoa, amaranth, corn etc.
I agree with increasing your fibre intake, and adding more vegetables each meal will fill you more than relying on wheat-based products.
I would try to get an intolerance test if you can, but I'm afraid I don't know the process, especially not during the pandemic when access to healthcare is restricted.
An advanced search on here will probably reveal many threads on the subject though.
I would say that a really good quality daily multivitamin won't hurt you, and perhaps an iron supplement for the week of your period, just to stave off any issues there. Also try to get outside for a walk somewhere between 11am and 2pm, even just for twenty minutes, will help by promoting good sleep in the evening. If you can, expose some of your skin to the 'sunlight' (haha- I'm assuming you're in Britain, and I know it's rationed here 
) for just 10-15 minutes will help your body produce vitamin D too.