How can i loose 20 lbs im 5'2 and weigh 120?

i wanted to get back from the weight i used to have before which is 104 i started running but it seems like its not working i started last week this will be my second week running for 30minutes 2 miles non stop but i dont know if its gonna work cuz i check my weight again after that week didnt loose even a pound im so desperate i juz wanted to feel good again