My company policy for PerDiem for MORE than one year is that it is listed and taxed as Block 1 income on W2. Are my business expenses away from my home state deductible?

I have been working in a state other than my home state for a few years and have been receiving per diem through a policy that makes it taxable income and it is included in my W2-Block 1 income.  There are NO indications on W2 that I receive Per Diem. There is no 1099.  I have been paying rent, utilities, etc. and other business expenses during these years and have not ever claimed business expenses.  If the business expenses are eligible, that would mean that I have approx. $12K expenses per year for the last 3 or 4 years. I now owe large amounts of money to the IRS back through 2014 and am curious if I should have claimed these business expenses or if it is even legal and proper.???