Hi. I Got My Period Last Month On 24.1. I

Hi. I got my period last month on 24.1. I generally get it 4 days before. However I have not got it till today. I am travelling to a few temples soon. My gp has asked me to take regesterone today two times and said that I may probably get my period by tonight. Is the tablet used to get the period? Are there any side effects ? What happens if I continue the same till I return from my trip?