Flunil & benfomet for "OCD" Session?

I have been diagnosed with OCD(obsessive compulsive disorder).. Doctor suggested me to take "Flunil 20mg & benfomet" to intake   1) what is OCD & why it comes??I have severe repetitive thoughts & over thinking nature since few months...sometimes thinking might go for hours and days It made me so discomfort and irritated,I have some responsibilities to take,but (over thinking & Unnecessary thoughts) coming & distract me so much   2)doctor suggested me to intake "flunil 20mg & benfomet, They told me to use flunil @ afternoon & benfomet @ night after dinner  Incase if I get drowsy during day times after intake flunil,they suggested me to take night along with benfomet,so I am taking two tablets at night time "Is it necessary to take both tablets without changing pattern daily"? Does it cause any problem if I change the time pattern from morning session to night session? please help me to get rid off those all problems which I mentioned above Please give me your valuable answers