My Mom, 88, Experiences Fluid Sacks On Her Side That

My mom, 88, experiences fluid sacks on her side that eventually go away. This has occurred several times. She experienced soreness in that location yesterday, but there was no fluid. Today there is fluid. She is very frail, 105lbs, and has heart problems. She has a pacemaker and takes the following meds: Allopurinol, Atorvastatin, Metoprolol and Nifedical. Thank you.