I've really only been doing situps, what should I be doing in terms of back excercises?
Things you really would want to consider adding would include leg lifts (wherein you keep your back on the floor and raise your legs). This targets lower abs.
Your sides can be targeted a few different ways. Side crunches immediately come to mind, wherein you lay on your side, with your lower leg extended and your top leg curled. You might also try sitting with your legs and torso off the floor, taking a weight (could be a jug of water, for example) and rotating it over your chest.
Lastly, for your back, you can lay on your stomach, keeping your feet to the floor and using your lower half to lever your torso upwards.
These are only some, and remember, don't over-do anything your first few times out. Hopefully they help you out though.