Finding what is and what isn't part of the OCD may not always be what you want to spend your time doing, but sometimes certain treatments or medications will help with the OCD but not for possible underlying problems which may make it harder to treat the OCD.
Say you also suffer from ADD or Clinical Depression, you will have to take some extra steps to tackle them along side of the OCD. Certain conditions run parallel to one another and can make it harder to treat the OCD. A Mental Health Professional will be able to distinguish what you are dealing with most and how different problems may be treated simultaneously or consecutively.
Depression is a good example of how hard it is to know whether the OCD triggers the Depression or vice versa. Both will have to be taken seriously in order to come to a solution. In most cases SSRI's (medications prescribed for treating OCD) will also help to treat depression, but this is not the case for all of them. You only have to have gone through a depression once to know it's something that can ruin any progress you may have made with your OCD.
The discussed disorders will have a short explanation and some useful links.
If they are a OCSD, this will be mentioned.
Go here for a table with OCD- related disorders and their different names and abbreviations, if any.