How To Treat Low BP,diarrhea And Vomiting?

I am a 30 year old female. I have been in good health but lately I cannot stabilize my blood pressure. It keeps dropping low and then going normal and recycling again. I am not dehydrated, do not have thyroid disease and I have no potassium deficiency. I am 5'11 and 120lbs....so under weight. Always have been. I have not had diarrhea or vomiting. I do not use drugs or smoke and I only drink on occasion. Please help. My most recent blood pressure was 103/58 which my norm is 115 over 80 and my pulse is 89 resting. I feel sluggish, have a head ache and my chest is heavy. My dad has PVc and my 27 yr old sis has AFIB with Flipped T waves. I had an EKG done Wed. and all is well. No infection or fluid in ears to lead to dizziness. 93/57 was my reading earlier after eating. Any ideas? Could this all be stress/anxiety related