The VA famously (and sadly) takes years to make up its mind about a veteran's disability claim. This is a period of anxiety and worry while the veteran tries to address mounting medical and financial problems, but there's not much to be done about their timeline.
What you can do is consider the following:
1. get a letter, postcard ANYTHING to the VA immediately stating it is your intention to submit a disability claim for your illness or injury. Whatever compensation that eventually is awarded dates from the time-stamp on your notification to the VA...so don't wait. Say "Dear VA: I expect to apply for benefits for exposure to military herbicides and (any other issues you may have.)" sign and mail. Couldn't be easier!
2. consider using the VA's Fast Track claim process, where you complete everything you're going to present, gather all your proof (doctor's letters, personal statements, medical records, line of duty determinations, EVERYTHING) and submit. This is a process where you declare to the VA that you have a complete claim and are willing to let them make a determination based on the total package you present and on what's in their files on you already.
3. get with one of the veterans service organizations - they are the professionals in this mess. The Disabled American Veterans, Vietnam Veterans of America, Veterans of Foreign Wars, etc., all employ highly-trained advocates to help you put your claim to the VA. They require a power of attorney to represent you, and these people are bull dogs! They really latch onto the finer points of VA rules and regulations and make sure your application is as solid as can be. They know the ins-and-outs of strategies such as Individual Unemployability, which can bring many veterans up to 100% disabled ratings. Not only is the 100% rating a better monthly payment but it also means complete medical care - eyes, ears, dental, everything. And if your rated disability is 70% or higher it also means nursing home care in your own community.
4. if you are ill, ask the veterans service organization to help you get medical care from the VA on a "presumptive eligibility" basis until such time as your claim is resolved.