Doxycycline, Vaccines, Long term Nausea

I am wondering if anyone has experienced what I am going through. Back in June, I had pneumonia - generally a healthy person. I was prescribed Doxycycline which I took for 10 days. Shortly after that I got the Shingles shot. Shortly after that I began to feel nauseous and that has continued on and off until now. I had two good months in September and October and then I got the COVID vaccine, and the nausea has returned. I have tried everything but it won't go away. I am having a colonoscopy tomorrow and then have a gastroenterologist apointment in February. I have no other symptons except for nausea. I am wondering if it is something to do with antibiotic attacking my gut and then when I get a vaccine, it exasperates that. Just wondering if anyone else has experienced this. The long term nausea is so debilitating.