Have Got Diarrhoea, Since Yesterday Afternoon. When I Have Been

Have got diarrhoea, since yesterday afternoon. When I have been to the loo, the urge to defacate is still very strong, almost unbearable. I'm lying in bed at the moment and it's constantly there, but I don't think there's anything to come out! This is deeply uncomfortable as I still have cramps in the lower abdomen and a powerful feeling of " butterflies" at the same time. I keep going back to th e loo, convinced the diarrhoea will start but nothing does! Any ideas? Have taken two Imodium tablets at 1.45 am and one an hour ago. Should I take another one?