Please understand that even if you follow the opinion that the niqāb is not obligatory, that doesn’t mean it’s permissible for you to post selfies or photos of yourselves (with your khimārs, or headscarves) where non-mahram men can see them. Many scholars have said that this is forbidden for women who wear niqāb, not to mention women who do not.
What’s worse is to post selfies (where non-mahram men can see them) while wearing makeup and jewellery or after applying Snapchat filters or the like, especially while posing and pouting.
Hijāb does not mean headscarf. The headscarf is called “khimār”. Hijāb means to cover, screen or conceal (one’s beauty). If this concept is properly understood, then you’ll easily understand why it is forbidden to do the above.
If you’re struggling with hijāb, keep striving and ask Allāh to increase your īmān and knowledge, and to make you steadfast. Also, instead of reading about hijāb, begin with subjects such as Tawheed, Aqeedah, Īmān and the descriptions of Paradise and Hell. A few good books to start with are, “The Fundamentals of Tawheed” by Bilal Philips, “The Book of Emaan” by Ibn Taymiyyah (may Allah have mercy on him), and the Islamic Creed Series by Shaykh Umar Sulayman al-Ashqar (may Allah have mercy on him). Once you’ve done that, you can read more about the hijāb, if you need to.
May Allāh make it easy.