I am very prone to sinus issues. This is what helps me:
Steam steam steam. Steamy showers, steam inhalation, even just a warm flannel over my face. So soothing.
I also do saline rinses, but honestly find steam more effective. Worth a try though.
Facial and scalp massage - I find this helps when they are clogged and need to clear. Tapping forehead and nose, massaging under earlobes, pulling ears out and wiggling jaw (this helps open Eustachian tubes which are often blocked).
Humming - loudly. Try a few notes to see which you can feel resonating in your sinuses. It creates vibration which again helps them drain. Best done in shower, partly for the steam, partly because it's less embarrassing somehow.
I avoid decongestants unless truly desperate, I find ibuprofen the most helpful. I see a previous poster said the opposite though, so I guess see what works for you. Antihistamine can also be helpful.
And yes, if you were prescribed antibiotics for an infection and it hasn't cleared, you need to go back to the prescriber.