As mentioned in different thread, i think you are having DoF issue because you are too close to the subject. I am newbie too..haha..but i have read of this issue where area of focus is sharp but starts getting blur very fast ..and played around with my 1.8 and noticed it too.
As suggested, at 1.8, it's best to have sufficient distance. Have you tried around 2.8? With the 1.4 or 1.8, there's quite a huge room for play between 4 and 1.4/1.8 with regards to bokeh and speed. Play around the zone of 1.8 to 4. Many times i have to remind myself that i dun have to just use the extremes. My humble thoughts and suggestions based on the little experience i have.