Yes.... this can be really difficult. The thing I have found most helpful is to wedge the syringe in the back corner of the mouth and direct the flow over the tongue and down the throat. Have you budgie tilted at the ideal angle to direct the flow if meds to where the need to be. Take your time getting the syringe in the perfect position to ensure theat your bird actually gets the full dose of the meds. Push the syringe fast and steady, but not forceful. I don't think sneezing is absolutely normal, that may be more of a factor of him clearing the secretions from his respiratory infection than from you giving the meds. Does he sneeze up stuff that looks like the medication? You should start to see improvement in 2-3 days, if you don't than I would call the vet for possibly another medication or to take you bird in for an injection. Good luck.
I posted this on another thread a few days ago, you may find it helpful. There is a video of us giving meds to our budgie:
"Sorry to hear little Bud is not well. We had to give our Penry a course of medication recently and it took us a while to get the hand of it. The first thing I will say is make sure you have plenty of time. The first couple days I was running late for work, and us being rushed made the whole situation more stressful on Penry than it needed to be. Second thing is be calm and patient. This will help Bud feel the same way.
We took Penry onto the bathroom, closed the door, turned the light off, and then caught him with a tea towel. You can use your hands but I preferred the towel because that tricked Penry into thinking it wasn't really us that was catching him, and we also used the towel to keep his eyes and feet covered to keep him calm. Then lodge the syringe in the corner of his mouth over the tongue and inject the meds quickly. Offer millet immediately so he doesnt cough the meds back up.
Here's a video of use giving Penry his meds so you can see how it goes.
Hope this helps.... let me know if you have more questions. This is actually a pretty difficult thing to do and no matter how good you are your bird will NOT like it. Hang in there and hope Bud gets better soon!!"