Can penicillin v cause diarrhea and gastrointestinal pain? i take penicillin v for my tonsillitis but i feel sick in my belly. thanks!

Possibly: You may be having an adverse reaction to the pen v or you may be taking pen vk which contains potassium to which some are very sensitive. Or you may be experiencing changes in intestinal flora secondary to antibiotics. Since you are not likely to be taking this for more than 10 days, if it continues see your doctor for further evaluation.