We appreciate the sensitive nature of this question.
Physical intimacy is very much connected to our broader relationship with our spouses. This may be a cue to ask yourself what is going on in your relationship. How has your relationship shifted since you gave birth? When do you feel love for your husband? How do you express it?
Desire is a combination of psychological and physical factors. We suggest you begin to address your decreased desire by increasing the psychological stimuli for it, i.e., investing in romance. Some examples are: planning a "date" (the planning can also go into a special night at home), music, flowers, chocolate, whatever works for the two of you. Discuss this and try different possibilities until you find some things that work. Consider periodically taking turns surprising each other. Sometimes just the experience of teamwork to improve your relationship can itself improve it.
Often, especially with women postpartum, a major culprit is fatigue. Take steps to get yourself extra rest when you have a date in mind. For example, you can try to get a nap in, or you can call on your husband to take a late-night or early-morning shift with the baby in advance of being together. Getting more rest may help you deal with the stress you mention, as might attempting concrete steps to address your stressors at non-intimate times. When you make time to be together, try to focus on your partner.
Physical affection need not conclude with relations. Try to build a culture of touch, where sensual, non-sexual touch is part of every day when you are tehorah. (If this sounds daunting, start with one extra-long hug each day.) To increase your feelings of desire and closeness, you could agree in advance to have physical contact without intercourse. For example, a massage is often welcome during stressful periods and need not be followed by relations. As you engage in this type of intimate touch, try to let go of outside standards for your body and focus instead on what it is capable of doing or feeling.
Since desire is a combination of the psychological and physical, it exists on a continuum. That is to say, sometimes you may feel "not at all interested", but it is unlikely that that is true all the time. Try to open your mind to the possibility of enjoying relations, at least from time to time, even if over all you don't feel interested. Keep in mind that, physiologically, it takes women longer to become aroused than it takes men. So give yourselves time for foreplay, intimate physical behavior preceding penetration.
If matters do not improve with the above efforts, it may be helpful to you to meet with a professional counselor or sex therapist. In America, you could start by contacting the Center for Female Sexuality, which has served many religious couples: www.centerforfemalesexuality.com. Referrals to counselors can also be found via Nefesh: www.nefesh.org. Your gynecologist should be able to refer you to a local sex therapist. Please feel free to get back to us.