I had this problem too. I kept sending my companions on missions and grabbing things that I could gather along the way, yet there were things I wasn't looting. Then a guildie told me that there is a Crew Skills Vendor (look at your map near the crew skills trainer, with vendors highlighted) Head to that vendor, and the one thing you have been missing from recipies is on there. Buy a bunch and you'll level fast.
Also, remember to get more recipies to craft at your crew skills vendor as you level. Anything with a grey number next to it, is not giving you xp. If you reverse engineer (icon in your inventory along the top tab) your stuff... you have a chance to learn new recipies that way as well.
Let me know if you need any other tips