I would retain a good lawyer, as Marion county is not known for its lenient judges. I would suggest calling attorney Tania Alavi at 352-732-9191 (http://www.abplegal.com/). She is a very well regarded criminal lawyer in that area.
Jail time is certainly an option for the judge to consider and the State Attorney to recommend. On a VOP, you are exposed to the full sentence of the underlying offense, in this case a first degree misdemeanor which has a maximum penalty of one year, minus any time already served.
If you were ordered to undergo random screenings there must have been some element of your arrest that included drug use, or at least an alleged or suspected drug use history or something to make that an element. By testing positive during probation you will be seen as having validated that you have some issue with drug use. One way to mitigate this is to seek out treatment. Having a bed ready at a treatment facility can assist in making the argument that you may have slipped up but that you are taking positive steps to rectify that.
What ultimately happens depends on the judge. You are entitled to a hearing on the violation but the standard of proof is lower than the criminal conviction standard and you will likely be found in violation under such circumstances as you describe. If you admit the violation, having that treatment plan in place may be helpful.
You do need an attorney for this. They will be able to negotiate with the State, if the judge is willing to accept a negotiated disposition, or argue any mitigation on your behalf. Any other supporters who may write or speak on your behalf could be helpful. But be prepared to do some time in the county jail as that is a distinct possibility.
And, if drug abuse is an issue, seek treatment in any event. Even just going to AA or NA meetings, which are essentially free, can be an extremely helpful thing to do to try and change your habits, and your life, and avoid just this kind of thing in the future. Good luck.