I really want to wear a niqab?

Salam alaikum dear sister, don't hesitate to make that choice. For it is the right choice. Allah Subhana Wata'ala will give you strength to overcome problems and peoples dislikes. Have sabr and tawakkul. Don't be afraid for your unborn baby, like other sisters say there are other ways to obtain enough vitamin D. The protection you and your baby get from wearing the niqab is far more costly. You are precious and your baby is precious, why not give your baby and yourself the protection of the correct hijab? Allah Subhana Wata'ala will reward you. Be proud, make your husband proud and be of inspiration for other sisters struggling with the same question: will I start wearing niqab now or will I wait? Don't wait, don't hesitate. You are never too young or too weak to start. Wearing niqab will strengthen your iman. If people harass you, remember it's not you who should be ashamed! You show piety and dignity by covering yourself, where other sisters exhibit themselves, offering themselves and harming themselves. Set a good example, especially for young sisters and your own child. Start wearing niqab now, so your child will know you as a niqabi and respect you inscha Allah.

Due to lack of vitamin D exposure, the niqab can cause rickets in an unborn baby. However, this is very rare.

I'm not sure of the law entirely in the UK, but in Australia we have a right to freely practice our religion. If you wish to wear a niqab for the sake of the religion you follow, do not let people who may 'dislike' it push you away. If you are still uncomfortable and hesitant to cover your face because of the general public, then try an alternative such as the hijab.

If you're going to be ashamed of it then don't bother wearing it. It's like being Christian and being hesitant to wear a cross on your chain. Either be proud of your religion and represent it, or don't at all.

There are other ways to obtain Vitamin D - such as going to an all-female beach or going outside in your back yard for some sun. Even opening the blinds to let in some sun light can help.

No that is not true, especially if a non-muslim told you; probably because as you said earlier, the majority of the people in the UK hate it.

As for wearing it, I think you should go for it- it'll show you have great courage and piety even in the most disgusting of times where people roam half-naked on the streets.