upper respiratory tract infection
"Doxycycline treats bacteria build-up in the respiratory area. 
The burning of this drug is only attacking the bacteria build-up, which means it's working. 
As with any drug wait 3 to 4 hours before continuing the second dose; after taking Doxycycline drink plenty water, and wait 20 to 30 minutes before eating, and resume drinking water.

On the second day only take Doxycycline once a day and follow above directions.

Avoid sugar, salt, dairy products, brain cereal, and acidic foods. 
Soup and fruit that are non acidic is great.
Your welcomed to look up your own foods. Bon Appetit"