A; I’m so, so sorry this hasn’t been dealt with long ago. Your mother-in-law is right. It’s highly possible that this is a psychological response to getting pregnant so young. But it’s also possible that something happened to you physically during the birth of your first child that is making sex so painful. Of course, it could be both.
The first thing to do is to have a very, very honest talk with your OB/GYN. Be as specific as you can manage. Ask for a thorough exam. Since your doctor has been focused on your pregnancy, it’s possible that a physical problem hasn’t been seen or understood. Also talk about whether you should see an endocrinologist to check hormone levels. It’s also possible that your body never fully recovered from pregnancy. ((That may be hard to determine right now since you are pregnant again.) The point is — get a complete and thorough physical workup to rule out an undiagnosed medical issue.
If you check out physically, it’s then time to seek out a mental health counselor to further explore the trauma issue and whether there are psychological reasons for you to be uninterested in sexual contact and in pain when you try. It would be a shame, indeed, for you to give up on the closeness and sweetness of a physical relationship with someone you love due to an unresolved issue from your early teen years.
You are only 18. You’ve jumped into adult life very early. You have huge responsibilities with a toddler and a baby on the way. I very much hope that you have a loving partner and that the two of you are finding a way to build a strong family. I hope you have support and practical help of older people who care about you as well. You’ve chosen a hard path but not an impossible one.
I’m very glad you wrote. That was an important first step to fixing the problem. Now please do take the next step. Talk to your doctor. Don’t give up until you have answers. With the right treatment, I’m reasonably certain that you can reclaim your physical self.
I wish you well.