Have High BP, Cholesterol And Two Heart Stents. Continuous Headache And Nausea Regularly. Could It Be Drug Interactions?

My mother has had two heart stents, has high blood pressure, and high cholesterol. She takes meds for all of this. She is 78 years old. She has continual headaches, nausea regularly, and a pain in her stomach area or lower abdomen. Some days she has to go lay down 4 or 5 times because of some of these symptoms. We think the headaches and nausea are side affects to the meds. The pain in her abdomen has been scanned...MRI, Cat Scan, etc. with nothing found. Although this pain comes and goes with intensity...so severe at times she has been taken to the emergency room. I am concerned about all the meds she takes and the interactions with each other. Can these interactions possibly be a cause of the pain in her abdomen? What kind of doctor should we seek that would analyze all the meds she takes and/or be able to recommend alternatives? Please send reply to YYYY@YYYY . Thanks.