What should I do about tiredness and loss of interest in my job?

Vacation/Re-evaluate. Have you been on vacation or took a break from your job? Also, if you lost interest in your job, maybe it's a time to re-evaluate your options? Talking to a career counselor might be helpful. Also, take time for yourself, try to not bring work home, so you'll have a differentiation -- work is work and home is home.