I Am 39 About To Be 40 And My Periods Usually Come About Every 25-28 Days

Hi, I m 39, about to be 40 and my periods usually come about every 25-28 days. The past year or so, they ve began with a smelly, brown discharge for the first day or so until the heavy cramps and bleeding start and after about 5 days it s over. Then, maybe 3 or 4 months ago the brown discharge/spotting started to come more frequently, like after only 22-23 days, lasting for 3 days or so until the blood and cramps come. This month, I have had the brown stuff for 6 days (started only 20 days after last menstrual ) and the real bleeding hasn t come. Occasionally I will find bright blood when I wipe but just a smear. I m in good general health, don t smoke, only drink one or two diet drinks a day & plenty of water, drink lite beer (2-4) every few days and I drink one hydroxycut drink mix every weekday. I m 5-8, 150 lbs, down about 25 lbs over the past 2 years. Any advice as to if I should be worried or if this is just the natural cycle of things?