Can my depression be because my husband isn't helping?

Helping with what? Long-term feelings of not being responded to or cared about, can contribute to depression. If you also have family history and are on certain medications -- or are using alcohol/drugs -- it becomes more likely. I don't know what you want your husband's help with specifically, or how this is affecting you -- so it could help you lots more to see your own fp doctor or psychiatrist about this.
No, but . People with depression have swings in their ability to perform. Sometimes partners interpret this as laziness. Or disinterest. They need to understand the mechanisms working in depression to have compassion and be of help. Your therapist or doctor may be able to explain the supportive role of a spouse in treating this condition.
Yes. Yes, having a baby is suppose to be a wonderfully happy time, but when one is up every couple of hours to feed and change diapers without any spousal help, then fatigue sets in. This may lead to frustration, resentment, and ultimately depression.