I usually work out in 3 sets of 8-12 reps. I'm not sure what your set/rep scheme looks like, but I like to use that sort of mid-range instead of a very high-rep range (15+ reps per set). I think a good way to figure out whether or not you want to move up to a heavier weight is: test it out! If you think your 5 pound DBs are too light (and they probably are), test out the next weight range. If you can get through 3 sets of 8-12 reps without failing, then you're good. If the last few reps of each set are really hard, that's an even better sign. If they're not, try something a little heavier.
When I started "lifting" (and I use this loosely--because I feel that until I began lifting heavier things, I wasn't lifting at all), I was using 5 pound dumbbells (DBs). I eventually found that I was a lot stronger than I thought I was, and that high-rep training all the time wasn't ideal. I'm currently using 20 lb DBs for most DB movements, though sometimes 15 or 10 lb ones (depending on which muscle groups I'm using--some are stronger than others!).
Ever carry a gallon of milk one-handed? That's about 8 pounds right there! Ever carry something heavier
than a single gallon of milk? I'm willing to bet you have! Women don't seem to give themselves enough credit when it comes to strength
Women who have small children and spend all day lifting their kids and setting them down, who use 3-pound DBs when they work out drive me nuts! Girl, you've been lifting a 30-pound kid all day long--I KNOW you can lift more than 3 pounds at a time! Sorry if that's kind of a tangent, and you may or may not have kids, but you're stronger than you think you are! Try it out!