Baby is six weeks and on Zantac?

We thought that Grace may have colic because she would scream all the time, fuss with her bottle, and spit up a whole lot. Yesterday the doctor prescribed zantac and we gave her the first dose last night. She slept for 9 hours straight after eating a six ounce bottle! this morning she woke and fed and fell right back to sleep. Anyone else get prescribed zantac and it worked really well. Did it continue to work? I hate seeing my daughter so miserable I am hoping this works!