There is no connection between neck pain
,diarrhea and diabetes.
Take rest and may take some anti inflammatory like ibuprofen
40o mg three times a day.
Local hot compress will help.
Take plenty of fluids to avoid dehydration
and wait for few days.it shall be alright.
You may take some proton pump
inhibitor like pantoprozole 40 mg twice a day before meals for 4 to 5 days.
You shall be alright soon.
If your symptoms worsen you may consult your doctor for stool examination and culture and then institute proper antibiotic treatment.