If the job is not what you expected and not even your cup of tea, stay put and learn as much as you can while you carefully consider your next move.

You never know when a new job isn't going to pan out, or circumstances change, and you'll want to return to your previous company. I myself have done this. While being a hothead about leaving a job may seem satisfying at the time, it's just not very likely to serve you well in the long-run.

One of the toughest situations to be in is when you are objectively good at something, but realize that it's making you unhappy and unbalanced.

If you must leave your job after three months - and I recommend staying a year unless you're totally miserable - then downplay the short tenure both in your resume and in interviews.