You see not upsetting anyone , after 3 days , I would eat a little rice because that is normal for my diet ..
What is normal for your diet , what do you feel like eating ...
You don't want to go hypo and yes on metformin you can ...it does happen ...so while you are not well you need to eat when you feel able , this is the time I would indeed eat a banana , again that is me and I have done so when unwell ...
You need to look after yourself ...you should not really take metformin on an empty stomach ...you might consider some medical advise ...
Hope you get well soon ...kat