bacterial infection
"I had Sinusitis for a week then went to doctors with severe headache, pressure on forehead , I told I  have a bacterial  infection, headaches, weakness, feeling lethargic. Had one tablet yesterday with a sandwich, one this morning with breakfast.  Seems to be fast acting, as my nose is now clear again, no sign of infection,  no pressure or pain,  I believe this is the best  antibiotic I have ever taken, feeling great today. With food also drank 200mls water. I believe  everyone is different,  I seem fine and can tolerate doxycycline medication just fine, no more pressure headaches .... yippee !"