I had asked for some additional information and have not heard back.
Extreme belching is most often related to a significant excess of gas or from acid reflux disease, also called gastroesophageal reflux disease or GERD. Neither of these conditions will typically cause neck pain or a headache, but it is possible that an acute viral
infection could cause an exacerbation in the gas or GERD. It is also possible that taking certain over the counter medicines for the neck pain and headache exacerbated acid reflux to cause the belching, which is why I ask whether any medicines have been tried.
For the belching, it would be OK to use a medicine for gas. The most common medicine for gas is simethicone, which is available in a number of different brand names over the counter. There also are certain antacids that also contain simethicone, and the antacids may help with GERD.
Treatment of GERD also can be better accomplished with a stronger medicine to suppress stomach acid, such as ranitidine
/Zantac, omeprazole/Prilosec or esomeprazole/Nexium. Antacids are OK if effective, and may work for mild cases, but more severe disease will usually need the stronger medicine, and it would be OK to augment the stronger medicine with an antacid.
For the neck pain and headache, the best over the counter medicine would be acetaminophen, but this drug is better because it is better tolerated by the abdomen. If the neck pain and headache were the sole symptoms, then an anti-inflammatory medicine, such as ibuprofen or naproxen, also would be a reasonable option, but these are the medicines (along with aspirin) that can irritate the stomach that I noted above
If these interventions
are not sufficient to ease symptoms, then it would be better to be seen.
If I can provide any further information, please let me know.