Barring any medical conditions you may have (I'm assuming you don't since you don't mention any) best suggestion is to ask your doctor for a blood test to determine your thyroid levels (usually by checking the liver enzymes) - whether it's hyper or hypothyroidism - which affects your metabolism.  Take notice of any changes in your diet, stress levels and lifestyle - proper nutrition and sleep is vital as you get older.

Above all, be an active partner with your licensed medical practitioner and communicate your concerns.  Make sure you have a doctor who pays attention to your health as a whole person and really listens you.  Especially one who is open to alternative medicine and herbal supplementation.

Take care and be well.