I think you might be having Antibiotic associated diarrhoea
. Your doctor is right. Normally , we have a lot of good bacteria in our intestines that keep a check on the growth of harmful bacteria. But what some antibiotics does is that it destroys the good bacteria that are actually helpful to us. With the good bacteria dead, it is easier for the bad bacteria to rule, producing toxins and making the person sick. That could be the reason for your diarrhoea and cramping and blood in the stool.
It is very important to get that result on the stool sample as it could tell us which bacteria is actually causing the problem and it can be treated accordingly. Some cases of antibiotic associated diarrhoea are self limiting. It resolves on its own , once the antibiotics are stopped, or with home remedies
. Some cases lead to complications like pseudo membranous colitis
Visit your doctor with the stool sample report.
In the meantime, rehydrate your body by drinking plenty of fluids like water, tender coconut water, bland soups etc. Instead of eating large meals, have frequent small meals.Eg, instead of eating 3 large meals a day, have 5-6 small meals a day. Avoid tea, coffee,soda, soft drinks, alcohol etc. Avoid deep fried, fatty food, high fibre food,spicy food.
Hope this helps. Get well soon :)