Ah.
Same happened with me first time I played. I got so beaten by Cerberus..
Go out and get the hintbook if you can, it's not cheating, this game is
difficult to master, but well worth it when you do. ^_^
You really should start over. In addition to not using Guardian Forces excessively (only when you encounter a big monster or a boss monster) you should take the time to talk to people, explore the garden network in the beginning, for example. It's amazing all the little things and foreshadowing you can notice, really. If you can't get the strat guide but want some advice, I'll be glad to help. I'm like.. the FFVIII masta.
If you don't want to start over, get the book, or take advice, I'm gonna jam some down yer throat. ^_^ The key to beating Cerberus is to equip your characters with Thunder resistance, and make sure one of your characters has DISPEL in thier spell inventory, he's almost impossible to beat without that. (If you still have early game weapons, later in the game is only gonna get more difficult.. going to the forest in the canyon where Galbadia Garden was will probably net you a few of the items needed to remodel.. oh.. and
play cards! It can make the game alot more enjoyable if you don't have to draw all your spells and get all your items from monsters! ^_^