Why am I not getting pregnant? What can I do to increase possibility ?

Do you have a regular period? Start tracking your period on an app and have sex on the Fertile window period. Itll increase your chances. Good Luck!

What makes you sure that those three kids are his? Did he get a paternity test? He may not have been fertile, and they may not be his.

After he had those kids, he may have gotten a vasectomy, and he may not be telling you, letting you think this is your problem. Or he could have had an STD blocking the tubes since he got his last partner(s) pregnant. The doctor is asking for his sperm for a reason.

In cases of infertile couples, 40% of the time it's the woman, 40% of the time it's the man. 20% of the time they can't figure it out or it's both.

As he treated the last mother or mothers of his children, so he will treat you. There's a reason he's not marrying you, he's not planning to stick around. Please don't have children until you're married. Also, studies show that children do better with slightly older moms. Even 21 is better than 18. Use this time to go get an education.

Hun, sometimes you just can’t get pregnant by that guy if your alleles don’t match up correctly it could be a dangerous pregnancy and your body will continually reject it

Why do you keep asking this? None of us know love. That's why you see a medical professional 

If you’ve been trying to get pregnant for a year, that means you were 17. That is incredibly stupid. Are you financially stable (YOU, not just your older bf)? Does your bf take care of his other 3 children? I think it’s a stupid idea to have kids at your age, especially since you aren’t married. If he hasn’t made a commitment to you, what makes you think he will make a commitment to be a father for the next 18 years? Unless he makes a lot of money, it’s unlikely he can afford to support 4 kids. I also doubt you make enough money at age 18 to support yourself and a kid. Most 18 year olds aren’t that mature either. You should be thinking about college, not babies. 

God is saving you from yourself.

A. I think you're crazy. Do you know what a baby is going to do to your life?

B. It's a VERY bad idea to have children with a man who isn't committed to you through marriage. That's not old-fashioned- it's just common sense.

C. Is he making enough money to support 4 children? Because he's likely to leave you, and the courts will distribute child support based on "first come first served."

D. I think you're crazy. 

What to do next is have your boyfriend's semen tested like your doctor asked. Just because he was able to father three children in the past doesn't mean he can NOW. Stuff happens.

By the way, why are you trying to have children with someone who already has three of them? Is he really rich or something?