It is really difficult for some women to orgasm during sex, especially without oral or manual stimulation. Are you instructing him where to go and what to do? Have you tried manual (rather than "friend") masturbation to find what you like where?
Have you tried having your husband use your "friend" on you? What about special lubricants, like ones that get warm or give a tingling sensation?
I agree with elephantdreams that it may be the Zoloft. How long have you been on it? The whole 12 years? Was having an orgasm easier before you started it or do you know?
I think you should go to your doctor who prescribes the Zoloft and ask if there is an alternative medication without sexual side-effects. Also, checking your hormone levels may be warranted. There are hormonal imbalances that can diminish sex-drive or make it difficult to have an orgasm, such as a thyroid imbalance. It's all worth checking. I have also heard of women taking small amounts of testosterone or using a testosterone cream to increase their sex-drive, but that may not be right for you.
The main thing is for you not to feel self-conscious and make your husband realize that it isn't his fault either. Getting discouraged is not going to help matters. As long as you enjoy being together, that's what counts. The rest can be worked on and be made better. But enjoying each other and the intimacy of it is the real point. Focusing on that may help, as well. Enjoy the moment.