I have had infertility issues as well as two miscarriages (we now have two beautiful adopted children, but for the first several years of our marriage we were childless). For me, it was hard to be around pregnant women (baby showers, etc.), but when my friends were genuinely excited and grateful I could usually get excited right along with them. Mostly I had a hard time with two specific ATTITUDES about being pregnant.
1. People who could choose what weekend they wanted to get pregnant (or talked endlessly about how quickly or easily they got pregnant) and didn't seem to have any sense that this extreme is no more "normal" than infertility - I always walked away with the feeling that they took their gift for granted and/or that they thought there was something wrong with me.
2. Those who didn't seem to appreciate the importance/priority/blessing of a child. The most hurtful moments I think I ever experienced on this level were when a good friend was at our house and went on and on about how inconvenient a time it was for his wife to be pregnant - primarily because they were moving to another state and this was going to make the move more difficult. He never expressed that he was even a little bit grateful for the ability to have another child, nor any real concern for the child (part of the hurt was that her previous pregnancy had ended in a miscarriage so I really felt like he should have known better). I wanted to scream at him that I would put up with a WHOLE lot more "inconvenience" than that for the blessing of having a child, and wasn't a child more important than his "convenience." Please understand,
it's not that I would want a good friend not to acknowledge difficult circumstances (husband out of work, sick parents, moving, tight finances, whatever) that make the timing difficult - it's the priorities involved. All of us, as moms, have days that are VERY inconvenient - kids throwing up on us, siblings fighting, whatever - and we talk and "vent" about them - but we (at least most of us) don't seriously wish our children didn't exist - at least not for very long. We love our children and recognize their importance. To me, pregnancy should be the same...having mixed feelings is fine, being worried is fine, being angry (for a little while) is fine, grieving dreams/plans that now can't happen is fine...but it is when the mom (or whoever) doesn't ultimately appreciate that there is an awesome and ultimately more important thing than "convenience" involved - a child - that I had and have a really hard time. It's all in the priorities and how the concerns are stated.
One more thing - I don't know your circumstances. You could have mixed feelings for a much deeper reason than the "convenience" reasons expressed by the friends that really bothered me. There could be health issues involved for you or the child, for instance, or the child might be coming into an abusive or otherwise dangerous situation. I don't think it would EVER have bothered me if a good friend expressed THAT kind of concern to me about being pregnant. I would want to know, because I care about my friends, too.