Suggest Treatment For Nausea And Diarrhea

Hello, I am 39 year old female otherwise healthy. A month ago I returned from a holiday in Spain and 5 days later felt nauseous and had diarrhea (although this only lasted a couple of days). I was never sick but felt sick and had stomach cramps and mild fever maybe a few times. I thought it was gone and returned to a normalish diet but cramps and nausea returned intermittedly. I then went back to a bland diet (BRAT type but when felt bit better included veg and green juices) and seemed ok. But it keeps coming back after I think it is gone. I thought I had turned the corner again as felt fine most of last week (apart from when I ate a sweet potato and feta tortilla and then felt sick for a bit). Then last night had pasta with a creamy sauce. Today I feel awful with the cramps and nausea back again. My friend in spain I was with also initially had the same stomach issues as me but he took antibiotics 2 weeks ago and I think is all ok now. We both ate supposedly fresh tuna 5 days before I had the initial bug symptoms and we also both swam in a hotel spa. I m wondering if either could have been the culprit. I did go to the doctor 2 weeks ago and they said to eat simply and try and ride it out which I thought had happened. They said to go back in another 2 weeks if not better which I will do on Tuesday. My digestion does not feel normal and not sure what best for me to be eating. My stools have been normal - maybe a little loose - but after eating rich food again last night and today they are definitely looser and I have had been belching and had stomach cramps again. I also got a cold last week on the back of thinking the stomach bug had gone, so thought my immune system was low so been taking probiotics. I thought the cold was on its way out but that has now come back too. Not sure what best to do. I will go to docs on Tuesday but just worrying about it for now. I just want to know is it normal to have a stomach bug on and off for a month - no real diorrhea after first few days and no vomiting at all. Is it just that my digestive system is sensitive still and needs more bland food. No dairy etc? Any advice would be gratefully received. Thank you.