Pregnancy Craving #3

I'm in bed and I can't sleep because I can't stop thinking about the most random food on earth, one I didn't even think I liked. I don't have the stuff to make it, and I'm pretty sure any tuna melt from a restaurant that is open at midnight is not the kind I want to be eating. 

Do pregnancy cravings happen more in the 3rd trimester? Or are they random he entire time? I'm just wondering if I need to brace myself, since I've only had 2 others this far.