Hi thinkingincodes,
I hope you know that you don't have to go back to work until you are fit and well. The most important thing is to look after your health, both physical and mental. If you reach the end of your sign-off period and are not well enough to return to work yet, then go back to your GP and tell them that your OCD is affecting your ability to carry out your normal activities, and that you need the GP to sign you off work for a longer period. (That is, if you are unable to return to work yet. Only you can be the judge of that.)
You GP can sign you off for a longer period; you can tell your GP how long to sign you off for. (2 weeks, 4 weeks, 8 weeks...only you know how long you need to be away from work.) If your OCD is interfering with your ability to do your job, then make sure you tell your GP that. Returning to work when you are ill is not a good idea -- in my own experience.
You might want to read some of the information packs on the OCD Action website, such as "OCD and Work -- Your Rights", and the information sheet for GP's about OCD, and "OCD and Accessing Treatment - Your Rights".
Did you know that OCD is classed as a disability under the Equality Act 2010? (Jude Wynne, the Advocacy Manager at OCD Action, discussed this at the OCD Action Conference last week.) Your employer is breaking the law if they discriminate against you because of your illness -- but the law only covers you if you disclose your illness to your employer.
For lots of infomation about work, OCD, and your rights, contact Jude Wynne and the Advocacy team at OCD Action.
Make sure you're being honest with your GP. If you're unwell because of your OCD, then tell your GP that you're unwell, and if you think you need more time off work, then tell your GP to sign you off for a longer period.
(And make sure -- by asking them -- that the GP has a good understanding of what OCD is, and what the appropriate treatments are.) You might want to print a copy of the NICE Guidelines off the OCD Action website (in "Resources"), and read it carefully.
I hope you start to feel better soon.