We don't use any birth control and still don't get pregnant but I have had 4 kids already by the same man?

Your question has been moved from the Construction forum to the Pregnancy & New Motherhood forum as your question has nothing to do with building.

Now, back to the question at hand.

You have 4 children from the same man and you want a 5th?

I also don't understand "curved" uterus. Could you mean tilted?

How long have you been trying for your 5th child?

Obviously you're fertile if you already have 4 kids, so what's the concern?

How long have you been trying? Have you or your partner had any health concerns since the last child? What are your ages now? How long ago did you have the last child?

It can happen where a couple will develop secondary infertility... where they have had a child (or more) and find it difficult to conceive again for a variety of possible reasons.