Congrats on being clean for 3 weeks! That is truly great! Now that you are clean, you will have more quality time to actually enjoy any activity that you pursue. It is very important that you stay clear of other people who are using. Think of it as doing something great for yourself by actively seeking support from others who are sober. Sober support networks are very important in recovery.
The list of things that you can find to enjoy is HUGE! I think I have a really big list of things that you can explore and try. I will go search for it now and I will come back and post it for you. It is cool.
Hang in there! There is so much in life for you to enjoy now that you are sober! You are in for some great memories and lots of moments to enjoy.