import re
regex = r"\*{2}Header2\*{2}\s*([^*]+)\s*"
test_str = ("**Header1** \n"
"thing1 \n"
"thing2 \n"
"thing3 \n"
"thing4 \n\n"
"**Header2** \n"
"dsfgs \n"
"sdgsg \n"
"rrrrrr \n\n"
"**Hello Dolly** \n"
"abider \n"
"abcder \n"
"ffffff")
print(re.search(regex, test_str).group(1))
aW1wb3J0IHJlCgpyZWdleCA9IHIiXCp7Mn1IZWFkZXIyXCp7Mn1ccyooW14qXSspXHMqIgoKdGVzdF9zdHIgPSAoIioqSGVhZGVyMSoqICAgXG4iCgkidGhpbmcxICBcbiIKCSJ0aGluZzIgIFxuIgoJInRoaW5nMyAgXG4iCgkidGhpbmc0IFxuXG4iCgkiKipIZWFkZXIyKiogIFxuIgoJImRzZmdzICBcbiIKCSJzZGdzZyAgXG4iCgkicnJycnJyIFxuXG4iCgkiKipIZWxsbyBEb2xseSoqICBcbiIKCSJhYmlkZXIgIFxuIgoJImFiY2RlciAgXG4iCgkiZmZmZmZmIikKCnByaW50KHJlLnNlYXJjaChyZWdleCwgdGVzdF9zdHIpLmdyb3VwKDEpKQ==