Generally, once you are sentenced it is very difficult to undo a plea. But if you want to pursue this you should contact an attorney right away. You may want to ask your attorney first. The problem with attempting to undo to a plea is that you tell the court you lied when you plead guilty.
Unfortunately, you are long past the time in which to attempt to have the court reconsider the sentence and your entry of a plea. Many individuals harbor regrets for decisions which seemed (back then) to have been, and perhaps still are, the right move.
Derek Brett, Esq.
The Brett Law Firm, P.A.
It will be tough to undo the plea bargain (just as you wouldn't want the State of Florida to undo their part of the plea agreement and say, "We change our mind and we now want ten years in prison instead of probation").
You have thirty (30) days to appeal the legality of your sentence, but I would be very careful what you wish for. While your sentence may not seem appropriate to you, receiveing a "withhold of adjudication" and no jail or prison time on a large Grand Theft can be (in many times) a very favorable sentence. Not only is your sentence a "legal" sentence (that you would have a hard time appealing), but it is also a "low" sentence and if your plea was withdrawn you would be looking at the original 5, 15, or 30 years in prison (depending on the value of the theft).
No Judge is going to care about the fact that "the only reason [you] plead [was] because you have a newborn son."
Aaron J. Slavin, Esq.
SLAVIN LAW FIRM, LLC