Welcome to health care magic and thank you for your question.
In my opinion you should consult your doctor. In the meantime you can do the following:
1. Start ORS
(Oral rehydration salt). Normally it comes as one pack in one litre of water (cooled after boiling). This ratio should not be changed as it matches the bodies natural salt levels.
2. ORS will help you in overcoming weakness because that is occuring due to electrolytes depletion.
3. Consider starting an antibiotic.
4. Consider starting cap omeprazole
20mg,once daily. Because black colored stool show bleeding in the intestine. It is nothing to worry as it can occur as the virus/bacteria damages the gut mucosa.
5. Take soft diet
I hope this helps you.