First off, it sounds like you probably need more direct clitoral stimulation, and you may need more intense clitoral stimulation. Your boyfriend's tongue, hand, your own hand, or a vibrator can provide this.
Many women find that they are able to have multiple orgasms when they use vibrators during sex play.
So I strongly recommend getting an inexpensive vibrator with adjustable vibrations, and experimenting with it during both your self-pleasuring, and in play with your boyfriend. The way many people have found helps to have longer orgasms is to provide a wide variety of stimulation to all the parts of your body that enjoy touch and sensation. In addition, the longer you pleasure your whole body, the more intense your orgasms are likely to be. This means exploring all those places that feel wonderful when your partner strokes, licks, or rubs them. Many women report having full-body orgasms when they experience prolonged stimulation all over their body that culminates in long and intense genital stimulation.