I too was really craving junk and carbs for much of my first trimester. This was my version of morning sickness: I'd feel vaguely nauseous with a very anxious hunger that seemed to only be satisfied by carbs and junk, the thought of anything else made me feel more nauseous. My diet before had been great, and I'd finally found a local source of kale in Nicaragua when suddenly kale became enemy number one. All this has passed now, EXCEPT the kale aversion. I did like others and tried to hide good stuff like leafy greens in my shakes, which I could still stomach most of the time.
In the midst of this junk-crazed morning sickness I started taking vitamin B6, which I'd read is helpful for morning sickness nausea (B12 helps with the vomits) - and it was like a MIRACLE. On the days I'd forget to take it, I would go right back to the grocery store runs for chips ahoy (which are expensive and not easy to find in Nicaragua!!) and thing I never even ate as a kid, like Aunt Jemima pancakes. It was nuts. But the B6 did the trick, I would HIGHLY recommend trying it. If it's in your prenatals it probably is too low a dose to be therapeutic. I took 50mg daily and it was perfect. You can take more, but I'd check with your midwife or doc if you think you need more than 50mg as there is an upper limit to what is safe (50 is well within safe). I'm no longer taking it as my body has finally adapted to the hormonal changes in 2nd trimester, but it really saved me for a few weeks there, I wish I'd started it sooner.
But, I agree that the baby will take what it needs - your diet will mostly just be affecting yourself. They take our iron right from our blood, that's why WE get anemic. They take our calcium right from our bones, that's why WE eventually develop osteoporosis (among other reasons). These guys know what they need and take it even when their moms don't or can't get it! I'm feeling the affects of that now, as after that first trimester junk-a-thon I have not yet gained even a pound at 19.5 weeks, while my belly is certainly growing. The little guy is eating my muscles to get the protein he needs! My butt and thighs are noticeably smaller - my husband is concerned about me losing my ass! So, now that I'm able, I'm eating lots of protein (greek yogurt in shakes, protein powders, eggs, meat, nuts, lentils, beans).
If you can sneak some protein in you, it might cut some of the carb cravings, as others suggested. Or try to trick yourself into healthier carbs, like whole wheats, sprouted breads, brown rice, rice crackers, and put some cheese or other protein heavy condiments (hummus!) on them. Easier said than done though, I know (I still want to eat boxed mac and cheese way more than before.... mmm thinking about that for lunch)!!