Is it against the law for an employer to ask me if I needed a day off for mental health?

I recently resigned from a job in corrections. I was under investigation for inmate/staff relationship, and accused of doing acts while working. This is false, I admit that I was probably flirty but, nothing more than talk. During an interview with one of the supervisors, I was asked if I told an employee that I needed a "mental health" day. Then I was further asked what I did during my time off. I was only employed for 2mos but, I worked and average of 16-20hrs overtime everyweek and earned sicktime. I also have severe depression & anxiety. I was burnt out and obviously stressed. I quit because, I was told by another staff member that several employees got together, and some inmates, to say I was innapropriate. This was extremely false, I've been in the same relationship for 7yrs.