I am using a time serious data and OLS estimation. My dependent variable is Log GDP per capita and my independent variables are female-to-male labor participation rate, female-to male graduation rate, Oil price and Trade. So when I tested for stationarity I saw that all of the variables are non stationary, I did the first differencing to make them stationary , however Log GDP per capita, FMLPR and FMGR are not becoming stationary I do not know why?! And what to do now?? I discovered this issue recently and the deadline for this project after three weeks. Also the error is non stationary.