oxycodone vs duloxetine

I have an autoimmune disorder that has caused many problems, most recently pleural effusion, that is fluid in the sac surrounding my right lung. Since this began in February, a liter of fluid has been drained from my body 3 times a week. I am also on 80 mg of Furosemide twice a day to deal with fluid build up throughout my body. There can be a lot of pain associated with all this. I was on a small amount of Oxycodone, 2.5 mg/ 2.5% solution every 6 hours. Pain Center doctors believe this is an appropriate treatment. However, my PCP does not want me on Oxy so he prescribed Duloxetine, starting at 20 mg once a day. Although that's a low dose, I think I have had a strong reaction. I already have Cervical Dystonia, but since taking the Duloxetine, there is a lot more stiffness developing in my neck, back, jaw... Also, a rash has developed in the area of the drainage catheter. Another factor in considering any treatment is that I am 79. Duloxetine is questionable in treating elderly and concerns about opioid addition become much less relevant. So I'm mainly looking for thoughts on the use of Duloxetine in my situation, its effectiveness and possible side effects. Thoughts on Oxy use would also be appreciated. Thanks.