Of course it's normal! You're not a baby-making machine! You're a woman. Your life isn't supposed to be about cranking out babies. Seven months ago you had your 4th baby. For heaven's sake, it's too soon to have another baby.
Your body needs a vacation from making babies. You need a better birth control method. The one you are using isn't reliable. If you're Catholic, then you need to tell your husband that an alternate form of intercourse is needed so that you won't get pregnant again.
I can't give you advice about this baby. But if you are going to carry it to term, you need to stop breastfeeding now (if you are), get help with the other kids, study exactly what you need nutritionally and make sure that you eat and drink that so that you can be healthy. Get the doctor's recommendation of pregnancy vitamins - you need them NOW. And GET REST. You just had a baby. Having another one is terribly taxing on your body and you have to give it rest.
If your husband doesn't understand this, tell him that a preemie with life-threatening problems, months in the NICU and doctors bills sky high should at LEAST be worth his attention. Don't let him push you around. Get help now.
Good luck.