Smoking tends to ease the symptoms of anxiety and OCD. At least it does for me. It's like a relaxation tool. Your bodies saying, "hey wheres my nicotine!". It's new to your body not to have nicotine in it's system and it triggers an anxiety OCD response. That will pass over time. The longer you stay away from it. Your body will get used to having no cigarettes. And your symptoms will pass. How long has it been since your last cigarette?
Its totally normal for you to have more anxiety/ocd since you quit smoking. Although this isnt a medical opinion, its not an accident that you feel the need to smoke so much, you probably always will. Smoking helps us ocd folks with our nerves, which is why so many of us are smokers. I think its safe to say that alot of other ocd folks are just like you and and me and we need our cigarettes to stay level and stay (relatively) sane.
When I tried quitting smoking before, it was litterally driving me crazy, so I gave up and let myself enjoy my cigarettes; and I have to say Im so much happier after accepting the fact that Im a chainsmoker. Yes its bad I know, but your asking about OCD and anxiety, and Im saying that smoking always helps me feel better, which is why I do love it so much, and probably why you do to deep down. Im amazed that you lasted 3 weeks without smoking, thats great for you if its what you want. Just dont beat yourself up to bad if you find yourself "taking 2 steps backwards" every now and then and picking up a pack of cigarettes whenever you need them, sometimes you just have to focus on handeling one thing at a time before moving on. Best of luck sweetie!