Most veterans rated 100% for PTSD are not able to work, but you are not prohibited from working.
If you received Total Disability due to Individual Unemployability (TDIU), by definition you are not able to work. In other words, you receive IU benefits based on your inability to work.
This article (also a podcast), on TheMilitaryWallet.com, provides a good explanation of "VA math", including a table you can consult to figure out your total disability rating: Podcast 004: Funny Math – VA Disability Ratings. When 30 + 20 Doesn’t Always Equal 50.
You can also use online disability calculators to compute your total disability rating. I think the easiest one to us is Calculating Combined Disability, provided by the Vietnam Veterans of America - Arizona Council. But there is also the VA Disability Rating Calculator, by MicroHealth, and HadIt.com's Service Connected Disabilities Calculator.
NOLO has a good article on their site, How the VA Rates a Service-Connected Mental Disability. You can also consult the official General Rating Formula for Mental Disorders (38 C.F.R.§ 4.130) in the Code of Federal Regulations.
Regarding filing a claim for an increase and the C&P exam that VBA will probably require as part of that process, here are some resources:
Advice for Veterans – VA PTSD Compensation and Pension Exam – Advice for veterans who have filed a VA disability benefits claim for posttraumatic stress disorder (PTSD), and have been scheduled for a Compensation and Pension examination (C&P exam). [Open disclosure: That one is on my blog.]
Veterans Benefits for PTSD – Wikipedia article with details on VA benefits for veterans suffering from PTSD. Comprehensive but succinct.
What to Expect at Your C&P Exam – Well-written article for veterans that explains what you can expect at your C&P exam and how to prepare on Swords to Plowshares.
What to Expect at Your C&P Exam (Video) – A 5-minute video produced by the Department of Veterans Affairs that describes what veterans can expect at their C&P exam.
Of course, the most important thing is that you receive all the help and support that you need. Are you receiving treatment for PTSD? Contact the Veterans Crisis Line for immediate help: Call 1-800-273-8255 and Press 1, or chat, or text with a professional counselor.
It does sound like you are having significant difficulties related to PTSD, based on what you wrote, so filing for an increase makes sense.
I wish you all the best,
Mark
Note: Nothing I write here should be construed as representing the views or policies of the U.S. Department of Veterans Affairs or the federal government. I contribute here as a private citizen who cares about the men and women who risk their lives to protect the rest of us.