Depends on many circumstances including the quantity, where located in vehicle. I have heard a lot worse criminal back grounds than three DUIs. However, you need to hire a good attorney in your area to discuss these questions in greater detail, including your defense of not guilty. The lawyers that post on this site are very good. I am licensed in Illinois and Wisconsin. I have included a link for the Indianapolis Bar Association.
The previous DUI convictions shouldn't have a huge impact on current charge. But you do need to hire an attorney for the possession charge as it is a jailable offense. Go to the top of this page and click "find a lawyer" and search for a criminal defense attorney in Indy.
I am sorry to hear about your arrest. You have likely been charged on a theory of constructive possession. Under Indiana law, if you had potential access to an illegal substance (most often times this occurs in a vehicle), you can be charged with possession of that illegal substance even though it was not on your person at the time of the traffic stop. Although you can be charged with possession of the item, the government still has to prove that you had potential access to it. This may be particularly difficult given where the substance was at the time of the search, who owned the car, how long you had been in the car, etc. You need a lawyer to defend this matter for you and challenge these charges.