It's unclear from your question if you have already had your surgery, but assuming you have, you know how your own personal recovery is coming, at least compared to other patients your surgeon may have cared for. Ask his or her nursing staff. Let's assume your drain(s) are out and things are healing well. I'm sure your surgeon has outlined various restrictions for you such as avoiding strenuous activities, lifting, and certainly nothing like sit-ups, crunches, jogging, etc. These all have times when they are allowed associated with them.
A road trip just over three weeks post-op carries only slightly higher risk than pre-op, or further down your healing path. That specific risk is blood clots forming in your legs from excessive kinking of your leg veins without periodic muscular activity to keep the blood flowing. Staying hydrated, flexing your calf muscles continuously while driving, stretching out every now and then, and getting out of the car each hour or so (in a safe place where you can walk a bit and move around that static blood) are all ways to minimize those risks. Your surgeon may ask you to take a baby aspirin, but check with him or her first.
Some patients have hypercoagulable states that increase these risks some (such as Factor V Leiden), and smoking and estrogen use increase the risks of clots as well. The real answer is probably known to you already, and even more accurately if you ask your surgeon while providing those little details such as how long a trip you are planning and just how your own recovery is coming along.
Feel the Force, listen to your gut (and your plastic surgeon), and don't risk messing up your $8000 operation if you aren't really up for travel at that point! That being said, if your surgeon agrees and you are doing well at that point in your recovery, have a safe trip and make sure you move around once you arrive! Best wishes! Dr. Tholen