You mention that you have a three year-old son. I would wonder how your relationship with your husband evolved from having only the two of you to the addition of a child. Rambunctious or not, young children are quite demanding of time and energy for both of you. Couples often fail to make the time for themselves that's needed. Also, if the responsibilities of the home and child care are not satisfactorily divided between the two of you, resentments may have developed over time.
Sex can also be an issue for couples with very young children.
Oftentimes the frequency of sex decreases following the birth of a child. The couple can then become stuck in this pattern to the frustration of both. The lack of sex can create friction between the partners, especially if sex was an important factor in the relationship before the child came along. Without more information it's hard to suggest other dynamics going on, but regardless of the causes, again it's the patterns of interaction that are going on right now that are the real problems. A professional couples counselor will be able to assess the dynamics and help you and your husband resolve the issues that are fueling this crisis.