If the pain occurs along with severe anxiety and /or panic attacks,it is probably secondary to the stress and anxiety.
This is especially so since your doctor/PCP does not find any problem either on examination or on investigations.
The dizziness,neck pain,headache and a sinking sensation along with palpitations and shortness of breath usually occur during severe anxiety or panic attacks.
If you do not respond to SSRIs like Citalopram,you probably need to be seen by a Psychiatrist who can take a detailed history and guide you further.
You may need counselling,along with Cognitive Behavioural Therapy(CBT).Drugs like antidepressants(Tricyclic Antidepressants) and SSRIs(like Venlafaxine,Duoloxetine) are useful for treating Generalise Anxiety Disorder and panic attacks.Regular exercise,a healthy diet,reducing stress by relaxing with family and friends,listening to music/going for long ambling walks will help.
You can discuss this with your doctor who can guide you further.If you are not responding to one SSRI like Citalopram,you may give a trial to other SSRIs/SNRIs.Drugs to reduce anxiety like Lorazepam/Clonazepam may help till the full effect of the SSRIs/TCAs is seen.