OCD is classified as an anxiety disorder. It is also a neurological disorder. Studies have narrowed down the Basal Ganglia- a collection of nuclei found on both sides of the thalamus- to be the source of where OCD originates in the brain. Basically it's like your thoughts and actions are stuck in a loop in the brain. That would explain the feeling of being stuck a lot of OCD sufferers feel at times. Also the basal ganglia controls "error messages" in your brain, or the feeling something is wrong. In OCD the basal ganglia activity is overactive or hyperactive, so you often feel that something is wrong, when in fact nothing is wrong at all.
So you're not crazy, you have a neurological difference in your basal ganglia, as compared with people who do not suffer from OCD. You have a neurological disorder. Even though most times, dealing with OCD you feel like you're crazy or a mental case, you're not, you're just someone who has a physical difference in their brains from those of non-sufferers. It can be worked with. A lot of the problem with OCD is over the years, as you respond out of fear or confusion to these false messages your brain is sending out, it becomes habit to respond in that way.
When you can identify the problem and break the habit, you gain control over what is controlling you. You will still have OCD, yes, and you may have to be on medications for the rest of your life, depending upon how bad your have it, but if you can gain control, you will be high functioning, meaning you can live a mostly normal and productive life.
Let's start going through the sub-types of OCD shall we?
Check it out the dedicated page here: What is OCD and what causes it?