Tell him.
Just tell him.
Honestly, it has gone on long enough and look at the state you are in! This is just daft, you need to tell him. He loves you. He wont care that you have "ruined the surprise", that will be the furthest thing from his mind knowing how bad you are.
If you tell him, what is the worst that could happen? He wont be surprised, big whoop. No about-to-be-parent really gives a toss about that, it is a healthy baby that will come out that is the big deal.
Imagine it in your head- how will be react? Do you really think he will fixate on you going off and doing this on your own, or do you think he will more be like "Bloddy hell, a boy?!! Thats fantastic, wow, a boy, I am going to have a wee boy, my god!!" and so on.
Then he might say, "I would have liked the surprise, but is this why you have been so ill? Lela, I am so sorry that I could not support you, you have be dealing with this on your own. Lela I love you, we can get through this, we are going to have a wee boy, and I will support you know matter what!"
You are in a partnership with from what you say an amazing guy, he not going to up sticks and leave you cos you ruined a surprise.
Love xx