For erosive gastritis
,you have to go for PPI inhibitors with the advice of your doctor.Along with it,a prokinetic drug has to be added.
Pain in the lower back side may be due to Musculo skeletal pain,Ureteric calculi etc.Cause of the pain can be diagnosed with Xray abdomen,Ultrasound
abdomen.If they are inconclusive,you have to for further investigations with the advice of your doctor.
Increased frequency of urination may also be due to Urinary tract infection
.Drink plenty of liquids.
Consult your Urologist
Wish you good health