What Medicament Can Be Given To A Person Having Afib With Symptoms Lethargy, Lightheaded?

I have AFib and taking Metoprolol for past 8 years. For the past 4 to 5 months my symptoms are getting worse.... severe sob, lethargy, lightheaded, extremeties feel so weak and I feel as if my head is upside down filled with fluid...also having difficulty sleeping. My cardiologist is tweeking my meds. I am now taking 100mg 2 bid and if anything I am more symptomatic. I do speak openly with him about my symptoms and he seems to think the 200mg is the answer. If that was true, wouldn t I be feeling better now and along the journey of increasing the med. I just turned 60 and last year was a thriving, ind. woman who planned on riding roller coasters until I turned 80y/o. I can t even walk to my car without stopping several times and completing daily functions. Also, is there a recommended dose?