Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. If you find the tablet too big in size then, you can break it into two pieces and can take half a piece at once and then the other half piece. Also yes, you can take Doxycycline to reduce infection in your sinuses. But as antibiotics are prescription drugs, you should get the medication prescribed by a physician. Along with antibiotics, you should also take an anti-inflammatory painkiller like Ibuprofen, decongestants like Pseudoephedrine, do saline nasal irrigation, steam inhalation and use a humidifier in your room. You can also be advised decongestant nasal sprays containing Xylometazoline or Oxymetazoline. Avoid spicy and chilled foods. Do warm compresses around nostrils. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Honey Arora