Is it okay to stretch when I am still sore?

You certainly don't want to cause more harm than good. Without an in-person evaluation, the exact reason behind your soreness cannot be determined. As your soreness cannot be safely assessed via the internet, specific recommendations cannot be made as to whether stretching would be appropriate under your current conditions. It's safe to say some soreness may be due to the new way you are using some of the muscles, though if any action causes severe pain stop the activity and seek guidance from your health care provider. Allowing a day of rest between stretching and yoga activities can help your muscles recover and support your overall goals. If you have only minor muscle soreness, consider using static stretching.