Acidity & Indigestion. Long can i take?

Dear Mam, just entered 21st week today.. I consulted a doc as I had severe heartburn and acidity, doc put me on Rantac 150mg.. I have been taking it twice from past 2 days, feeling much better but if I eat anything after 7:30pm, doesn't get digested and I throw up.. I'm able to eat morning and afternoon.. I'm having this sickness from 3rd month onwards.. not able to get in touch with doctor again.. there is some technical issue online.. from 3rd month, I'm not having normal days and I'm so scared to step out coz of nausea and vomiting.. and also this is an IVF conception and I'm not allowed to walk too much.. but I try and walk little after every meal.. been eating small meal with ginger etc but still.. is taking Rantac twice safe & for how long can I take ? And also how to get rid of vomiting and eat well..