I have got a sinus infection for over a month. I've taken1000 mg of amoxicillin for 28 days and it has still not gone. What should I do?

Amox not great. Amoxicillin is not a great drug for sinusitis. Amoxicillin + clavulante (augmentin) is preferred. A short course of steroids (prednisone) may be helpful as well. But if you have had symptoms this long, I would see your local ent. There are some newer technologies to open your sinuses up in the clinic... Using balloon technology like angioplasty: acclarent. Com.
See an ENT. Inflammation of your sinuses can be prolonged and uncomfortable. After being treated with 4 weeks of antibiotics, there likely isn't any more infection, but inflammation may persist due to your bodies reaction to the infection. Other medications can be used. Surgery may also be helpful.
Agree-tough case. These are all great answers. Additional considerations for your general health: take probiotics. After a month of Amoxil 1000mg a day your gut needs probiotic help! Also be sure you are on vitamin d...It helps with the immune system. It won't cure sinusitis but will help your immune system deal with the inflammation. Consider craniosacral therapy to open the sinuses and allow draining...
Tough Case. You probably need to see an ent. You may need further imaging, endoscopy and other treatments. Sinus infections can be very difficult to treat. See pcp or ent. Appears further evaluaiton and treatment is warranted.