“ I think I saw wearing of hijab long before the early 1970s. I’m not sure, and the creditability of this article is in doubt to me. ”
These sentences don't seem very connected, because the article referred to in the second doesn't fit with the first sentence. They could make sense in a larger context, though. In the second, you should say 'credibility'.
I think I saw hijab worn long before the early 1970s. I am not sure and I doubt the article's credibility.