Hi thanks for your question.
Doxicycline is a antibiotic which is known gastric irritant.Since the tablet got dissolved in your mouth and throat,it has caused sever esophagitis
(iiflammation if food pipe) and gastritis
(inflammation of stomach) Which is giving you punched sensation and pain in you chest.
Relax there is nothing to worry.
You need to take antacids and proton blocking pump blocking drugs(acid blocking drugs) like pantoprazole
for a week.
Yes asodophills,yogurt and milk all help in growing the good bacteria,killed by antibiotics.
Hope this answers your question.