I Am A 52 Yr Old Female Athlete. I Train

I am a 52 yr old female athlete. I train and compete in 1/2, full marathons & triathlons. I have high normal BP. 128/85 to 130/88. I am currently taking an ACE inhibitor at a low dose. I have a nagging pain in my upper left side in between my arm pit and breast. It has been there on and off for a couple of months. When I start out on a run it is worse but then eases up within a few miles. When I told my doctor he laughed it off with out pursuing it. My weight is also in normal range. It worry's me but he is not the first doctor to discount my symptoms because I am so active. They ignored my high BP for 3 years saying it was probably coffee. Any ideas on my next step?