can the state bring up priors in court if unrelated to charge you are on trial for

I am fighting a 2nd degree petit theft charge for allegedly switching tags on items that has been mishandled at every turn. The store loss prevention people inflated the amount, took my receipts so I have no proof of what I paid on the items which has not been refunded or credited to me in any way. The police officer didn't know what to charge me with and state attorney and judge tried to wrongly convict and sentence me for 1st degree even though I went to the clerk and had the charge amended because the police report stated it was less than 100 dollars,. I had to get a public defender. The APD I was assigned has no criminal law experience . ALL her Law school and internships are in tax and probate law she got the APD job right after passing the bar in 2017. I am disabled I can't afford an expensive atty. I Ave no prior theft charges and what little I have was withheld adj. or dismissed after pretrial by a judge over 10 yrs ago. What can I do? Overwhelmed and lost.