Well welcome! This is a good group of very talented artists and I hope you stick around.
You have a very nice start here. There are a couple of things I would suggest looking at first if your ultimate goal is realism. Shading is uber important. I would practice on that using everyday objects. We have a member here who often suggests using a pool ball and that is an excellent suggestion. Boxes..just day to day objects. Keep a sketchbook and draw daily the things you see and focus on your shapes and shading. That foundational work will go a long long way.
Also important in realism is to eliminate outlining. There are no true outlines when you look at something in real life. That is where learning to shade well comes into play. Your shading becomes how you define your subject matter.
I will say that (for me) portraits are difficult. You have to get the proportions just right. The eyes look a little too large in this particular piece however the fact that you were able to achieve what you did after only a weeks practice is very very good. I look forward to your future drawings.
Keep up with the sketchbook..draw daily and draw everyday things you see..don't get too ambitious to start off with..start small and try to master some basic skills and move up from there.
Nice job and once again..welcome!