Currently 37 weeks and about to pop, and had the same issue through the first and second trimesters. I had to relent and let myself eat what I could, bagels and macaroni, cereal, oatmeal, and milk. Meat was just repulsive and though previously veggies, salad and avacados were my regular fare, I could not, I mean COULD NOT make myself do it. I've always prided myself in my ability to basically eat anything, whether I liked it or not, purley for its nutritional content, but during this pregnancy its like someone was trying to get me to eat a live spider when it was just a grilled chicken salad.
All this being said, once I reached the 3rd trimester I decided I had enough strength to cut out the carbs and gluten and start the rebuild toward at least 80% paleo. Surprisingly, I am doing pretty well and have leveled off on the weight gain and have regained the clarity of mind I get from a gluten free diet, considering I have a pretty intense reaction to it including water retention, depression, and nasal congestion. I thought perhaps it was the pregnancy causing this, but once I cut out the gluten I've found it to have been the culprit.
Basically, do what you need to do to get the nutrients and vitamins needed to sustain your pregnancy in the beginning, considering the risk of miscarriage and such, and forgive yourself because the repulsion toward certain foods is nearly impossible to overcome, considering the hormone insanity going on in your body. Then if you can around the 7th, 8th month try to retrain yourself gently in preparation for the reclamation of your body, knowing your baby has developed to a little more self sufficient place and when you reach full term around 37 weeks your off the hook even more because the baby is ready to enter the world and full term, so you can be you. I'm still having a bowl of mini wheats, some yogurt a glass of milk here and there and I am really digging slim fast for keeping my sugar from dropping, but have really cut out the bread, I was super psyched when I had a low carb burger from hardees a few weeks ago and it was good with the lettuce, even though I can't do tomatoes still.
Your not ruining anything, your body was properly primed with your paleo diet, and you can return to it after the baby is born. What your body is asking of you is a bit out of your control, and it won't be the last time your child will make you do something he/she wants instead of what you want:)