You're level 20. Don't expect to be rich at this level. At level 20 I had approximately 20k, then I started crafting (as we all know that eats your income). By the time I hit 30 I had over 100k. I was able to maintain a healthy crafting schedule, buy a speeder license, increase my inventory size (twice for a total of 25k) buy a few upgrades... and I still had about 30k left. I made back everything I spent in a day. Now I'm making roughly 100k a day.
You want to know what the secret is? There is no secret. I crafting, due research missions, hunt, run nearly every mission I come across (excluding most Flashpoints) and I loot just about every mob I kill. Sell your trash loot and you'll make a bundle. I have not done any pvp, nor have I sold anything on the market. I buy items regularly and occasionally waste money on items that I don't need. And yet I still make about 100k profit a day.
By the time you hit level 30, you'll probably be averaging 40 - 60k a day in credits if you loot and sell everything you kill. If you have a problem with having to constantly loot mobs, turn on the auto-loot options and you won't have to deal with it so much.
P.S. I forgot to mention, my skills are now costing me about 22k each (averaging 2 - 3 per level) and I still finish each day with about 120k in my pocket.