Welcome to healthcare magic!
You have got doxycycline induced gastritis
which is a well known side effect of this drug.
You have probably a tendency for acid peptic disease
and may be a pre-existing gastritis which has flared up.
You should consult a gastroenterologist
, he would know the regimen for you to cure this trouble.
You should avoid doxycycline anymore.
I hope this advise would be helpful for you.
Still if you have any queries or doubts, please write me back,
I would be happy to solve them.
Wish you a great health!