The anti-biotics will make you extra sensitive to sun, you could burn very easily or get a "sun rash", like prickly heat. No fun.
But the best thing for sinus problems of most sorts seems to be nasal irrigation, either with a neti pot or a bottle irrigator. Easy to come by here in the States, or on-line. Not sure about Britain. It uses saline solution you make up yourself to flush out irritants and infectives from the sinuses. Sounds worse than it is. Anyway, usually that will get rid of whatever has your sinuses in a fit and then your body can overcome the problem sans MD.
I had many years of "sinus trouble" with all the infections, sinusitiis, etc. Wish I had known of this sooner. It works.
Glad to hear you are better. Take this as a time to get prepared if you are subject to sinus problems.
Then you wont have to suffer so next time round.
Ah, poor you. I hope you are feeling better now. I know how painful sinusitis can be. I must admit that I just take paracetamol. It opens up the sinuses and lets the gunk out. Not very pretty and you get through shed loads of hankies but it seems to work for me.