Since my treatment my sex drive is lower, why does this happen?

More specifics. There are numerous causes attributed to lowered sex drive, including physical, psychological, stress levels, medication, medication interactions, relationship issues, etc. What treatment are you referring to in your question?
Changed hormones? A drop in testosterone will lower sex drive (in both men and women). Also, much of sex drive is psychological, so any changes in happiness or stress will alter sex drive. Your question was not clear, so please send in another question to healthtap, and include some details, so our medical experts will be able to better answer your concerns. Thanks!