Hi.
I understand the concern that things seem to be getting worse and there doesn't seem to be enough done to address the issue.
First, you should look at your symptoms. If you are improving and the Xrays are nto - you should be cognizant that the Xrays tend to lag behind improvement of the clinical picture. And ultimately, the treatment should be directed on you, not the Xray. In general, if you are doing well you shouldn't be alarmed.
Second, performing a biopsy on the lung not aiming for a particular solid nodule would likely not yield anything pertinent, so the risks of getting a complication due to the biopsy procedure would likely outweigh the chances of getting answers.
I see no harm in a second opinion.
Stay positive.
a second opinion is always a good idea. but there isn't reason for biopsy if there's not any lesion/mass/thing to put a needle in. talk to your doctor more!