While there is some evidence that you have good immunity after having Covid and one dose of vaccine, according to Dr Fauci and the CDC, the decision is "under review" and the recommendation has not yet changed. Specifically, whether there is a difference in how long the elevated antibodies last with one or two doses is not known, and is being studied. My daughters both had Covid last year, and elected to get both doses of the vaccine because they are health care providers and wanted the maximum possible protection. They both had reactions to both doses of the vaccine, it was worth the discomfort.
I looked at the time frame between your injection & the reaction of dry mouth, etc – 15 days – and I would not be certain they are related after that length of time – typically side effects appear in 12-72 hours. What makes you think there is a connection? The post-Covid symptoms you mentioned are experienced by about 30% of those who get the virus, and are not caused by the vaccine, which has no virus in it.
So you are correct, there is conflicting information. Only you can decide whether to get a second injection, and arguments can be made for both decisions.
I'm sorry there is no definitive way to advise "yes or no" – as with all things Covid – stay tuned for updates…