Does using VA health care instead of my job's insurance help with supplemental or secondary VA claims?

There is no VA rule requiring you to get all or even most of your medical care through the VA in order to file or win a claim. What matters for a disability claim is the quality and completeness of the medical evidence, not which insurer paid for it. Records from private doctors, urgent care, specialists, or employer-sponsored insurance are just as admissible as VA treatment notes, as long as you (or your representative) submit them or authorize the VA to request them.

That said, there are practical reasons veterans often lean on VA care once they are already receiving VA disability compensation. VA treatment notes are automatically part of your claims file, so you don't have to chase down records or submit release forms the way you would with an outside provider. VA clinicians are also generally familiar with service-connection and secondary-condition documentation, which can make it easier to get diagnoses phrased in a way that supports a claim. But this convenience does not mean private records are weaker evidence, it just means less paperwork on your end.

For the symptoms you're describing, fatigue, weight gain, insomnia, and brain fog, if a doctor suspects a thyroid disorder such as hypothyroidism, the key steps are the same regardless of which insurance pays for it, get formal lab-confirmed diagnostic testing (TSH, T3, T4, and any relevant antibody panels), get a clear diagnosis in writing, and get a treating physician's opinion connecting the thyroid condition to your already service-connected conditions if you believe it's secondary rather than a new standalone claim. A secondary condition is typically filed with a nexus statement showing it is "at least as likely as not" caused or aggravated by an existing service-connected disability, using VA Form 21-526EZ for a new claim or VA Form 20-0995 for a supplemental claim if you've already been denied on a related issue and have new evidence.

Since your symptoms are affecting work performance and safety, it's also worth discussing accommodations or reduced duty with your employer separately from the VA claims process, since that is a distinct legal issue from service connection.

As a next step, get the thyroid panel done as soon as possible, whether through your employer's insurance or VA primary care, and once you have a diagnosis, ask the treating provider for a written opinion on any relationship to your existing service-connected conditions before filing the secondary claim.