Text function for dynamic reference to select different sheets

Hello everyone

I'd like to ask if it is possible to make dynamic reference in formulas like in attachment.
My point is - I got many formulas with external reference to another workbook. Workbook from which data is taken has sheets named 01.2019; 02.2019; 03.2019; 04.2019 etc.
So in formulas I have to select sheet for right month. Is it possible to make it dynamic - based on what is written in cell G4? So when G4 says "06.2019" all formulas ref to June and when G4 says "07.2019" formulas ref to July.