Is too much sex bad for your health?

Yes, but how much is appropriate for you depends upon your age, and frequency should decline with age. Also, sexual intercourse is considered to be more depeleting for men than for women. Excessive intercourse depletes Kidney function and if kept up over many years will seriously damage the long-term health.  

In men, ejaculation causes the loss of what is considered to be a precious fluid called Jing.  Women lose less Jing during intercourse than men, but instead lose Jing from miscarriage or abortion.  

Symptoms of Kidney deficiency include chronic low back ache (not just from the activity of intercourse itself), sore or weak knees, fatigue, poor memory, feeling cold even when in a comfortable environment, spontaneous sweating (cracking a sweat while doing nothing), dizziness, and tinnitus (ringing of the ears).  Long-term Kidney deficiency can lead to other more serious conditions like stroke, diabetes, arthritis, sleep apnea, and Reynaud's syndrome.  

Once the Kidney function is depleted, the entire immune system is adversely affected which makes the body much more susceptible to contracting viruses like shingles, influenza, respiratory or digestive allergies.  Furthermore, if you are already ill, say with cancer or another serious disease which requires the body to fight, then having too much sexual intercourse will unquestionably make it more difficult for the body to sucessfully combat these diseases.