Its been 8 months since me and my husband have had sex. I feel like I have no sexual desire especially when we do have sex because it hurts really really bad after my husband sticks his penis all the way in it feels like sharp knives carving in side of me. I don't understand why it hurts so bad and when this happens I just don't want to have sex.

It means that you need to see your doctor for a check-up to make certain that you are healthy. It will take an examination and testing to know if there is a physical/medical cause for your pain.

Have you talked with your husband about the pain and why you seem to be uninterested in sex? If not, be honest with him. It might help reduce any stress over the situation that you may be experiencing which might help ease any tension that could be making matters worse.

I suggest waiting on having sex again until after you have seen the doctor.

Aside from lack of lubrication and emotional considerations:
A portion of bowel or bladder can bulge into the vagina, or you could have a cyst, or any number of conditions, easy to find out on exam.
You could have a pinched nerve in your abdomen, which is difficult to detect, but you could experiment with an object (carrot etc, or your husband's fingers) to see when it hurts.
So yes, see a doctor.

According to the Mayo Clinic's website the most common causes of this condition--known as dyspareunia--are 1) insufficient lubrication--you may need more foreplay, 2) hormone inbalance such as after giving birth and 3) the side effect of a medication such as the Pill or blood pressure medication.

Painful intercourse (dyspareunia): Causes - MayoClinic.com

Yeah, you need medical checkup.