Could my "Doxycycline 100mg tablets" pills cause this?

Hi, welcome to the ehealth forum and I am glad to help you.
You seem concerned by the pain and burning under the ribs and pain during swallowing of food while being on doxycycline therapy for acne.
The most common doxycycline side effects are gastrointestinal problems including dyspepsia, nausea, and diarrhea.
Headache, painful menses, renal toxicity primarily elevated BUN/CR, and skin or tissue discoloration are fairly common doxycycline side effects.
An unusual doxycycline side effect is sometimes very severe esophagitis, really an esophageal ulceration, that is caused by not washing the pill down with enough water and allowing the pill to start to dissolve in the esophagus that leads to erosion or ulceration of the esophagus. This can cause severe pain with swallowing that is commonly seen in emergency rooms and primary physician’s offices.
Therefore,I strongly suggest that you consult your personal physician for the same and rule out the possibility of esophagitis as the same is not possible online.
Hope this helps. Take care.
Note: This post is not to emphasise final diagnosis as the same cannot be made online and is aimed just to provide medical information and no treatment suggested above be taken without face to face consultation with health care professional.