EllB, Only you can solve your orgasm difficulty. It is not easy graduating from pillow humping to a more 'natural' way of experiencing orgasms., especially if you grew up humping pillows. Your body grew accustomed to that way of pleasuring yourself and your nerve pathways got developed to carry these stimulation signals to your brain. Your brain is also instinctively associating you straddling your pillow with sexual pleasure.
The first thing to remember is that your clitoris is your primate orgasm organ, just like a man's penis is his primary orgasm organ. This is not saying that you cannot orgasm any other way. Just that this is by FAR the most likely way you will orgasm.
The second thing to keep in mind is that masturbation is much more than just rubbing your clitoris. There are a lot of tension building up in your genitals and body during masturbation. When you are riding your pillow, this happens automatically as you are on yur knees and using your upper leg muscles top rub yourself on your pillow.
When you flip over on your back, this change.You will now have to do things to increase the tension in your genital area. You can tense the muscles or pump your legs open and closed. You also have to concentrate on letting the tension build and build. If you need to read a story, look at pictures or watch a video, by all means do so. But do NOT relax your lower body muscles until you go over the edge and start to orgasm. Also do not think of other things. CONCENTRATE on the feelings in your genitals and making the tension increase.
It will take some time for you to change the way you orgasm. Don't give up. Try different strokes, different pressures, different speeds. What is important is to not directly touch your clitoris. touch it through your clitoral hood, around and beside it. Humping a pillow does not directly touch your clitoris but provides very broad indirect stimulation of your clitoris. So using your flat hand to stimulate your genitals might help.
Take care and happy hunting