I have been on this antibiotic for pneumonia for a week. I alread...

I have been on this antibiotic for pneumonia for a week. I already have a possible ulcer and have a prescription for zantac. I am on 100mg BID for two weeks. Since taking this medication my ulcer has become much much worse with frequent heartburn and a lot of drowsiness/lethargy. I feel like I float through my day and am confused and using the wrong words a lot, and just not paying full attention to anything. I have a constant pain right under my sternum that flares up and a lot of mid to lower back pain, esp. at night. I have had a headache for the last four days. I did some research and found that ANTACIDS SHOULD NOT BE TAKEN WITHIN TWO HOURS OF DOXYCYCLINE!!! Bummer for me, since I have been drinking Mylanta like it was my only source of hydration.