Dear Gloria,
I am humbled by your faithful avoidance of contraception amidst your difficult circumstances, and your desire to do the right thing, despite the challenges, and confident that will bring you happiness more than resorting to immoral but more expedient solutions.
The key to being able to restore full marital intimacy with your husband is excellent guidance in the use of NFP, and ultimately, faith that God is the source of all life, and will not abandon you. I sense you have experienced the latter, despite your fear and anxiety, and in time and with good instruction, you can gain confidence in using NFP in your marriage. It really is the only solution that will lead to true happiness in your situation.
Reading about NFP, even learning NFP from information gained on the internet or written materials, is just not adequate, especially in your situation. You really need to learn with the expert mentorship of an experienced teacher. And I would not be surprised if your cycles reflect some hormonal abnormality, based on your pregnancy history. The strong desire to avoid a pregnancy for the time being, given the health challenges you are coping with for existing children, is best met by becoming an expert on your fertility. And an unintended, but possible bonus of doing so, is that it is possible you may actually identify hormonal issues that can be addressed to improve your own long term physical and emotional well being, and improve your health and ability to go full term in a future pregnancy.
You will not serve your marriage by settling for any less than full intimacy (either by contracepting your intimacy, or by substituting with other acts in an attempt to achieve union without its procreative nature).
Modern Natural Family Planning is 97-99% effective, so there is no contraceptive that is going to be a more effective option for you. So not only does NFP the best option for your own health, and have potential for being the tool to identify health issues you may be having, it also is the most effective means for avoiding a pregnancy for the time being. In addition, it will permit your husband to share the responsibility and decision making with you, strengthening your relationship.
While NFP is already effective and scientifically sound, you can work with your teacher for guidance on applying in a way that can achieve the highest of effectiveness. This will mean less opportunity for intercourse, but permit you to resume intercourse with less anxiety. Some couples with very serious reason to avoid pregnancy, like yourself, use only the infertile period of the cycle that occurs after confirming ovulation. There is even the option, in very serious cases, of confirming ovulation with a one time progesterone level in each cycle, to lessen anxiety and confirm the remaining cycle days are infertile.
I would like to help you find the Professional you need to take this walk with you. Please call our office at 831-443-3746 so we can discuss the options, and I can answer your questions more specifically, and we can get you connected with the right Professionals to implement what I am confident will be the long term solution to your dilemma.
Sheila St. John