My Fiancé and I have been together for 2 years.
In November last year we broke up and we both saw different people.
We got back together in march this year.
This girl he went out with has now got a 2 month old baby girl.
She doesn't know if the baby is my fiancés or her ex boyfriends.
Everyone has their different oppinions on it but me personally I don't think it is is because the dates don't really match and he did use protection.
Everyone has been talking about it over the past few days and they think she sort of looks like my fiancés niece but I don't really think she does.
I recently jave just fallen pregnant to. I'm 10 weeks.
Also we have been trying to have a baby for 1 year and a half.
That's y this is scaring me because we tried so much and if this baby is his then why does she have sex with him once (thats the only time they did it) and fall pregnant but it takes me 1 yr and a half.
I'm feeling very upset about this and I don't know how I should feel.
I just want us to be a family and be happy.
I really need some help on this.

I suggest that you ask him to seek a paternity test, that will tell you definitely whether the baby is his or not.

Also, some women can get pregnant the first time they have sex, other women try years without success, it's just every woman's body is different and it's not your fault or anyone else's, just nature.

Well. It can take one time, it can take 100 times to get pregnant. So that doesn't answer the question. The only sure way to know is a paternity test. That's the best way for everyone. What if she starts to accuse him and wanting child support.. Well.. Proof it to yourself! Let him know that you are worried about it, and that it's an important matter.
Another thing, if it is his, are you both going to be a part of that child's life? That's another serious matter. Don't risk it, find out for sure. Take a paternity test.