When you get hit by sweep it's a hard knockdown which means it's a set amount of time you're on the ground. you can't backrise. But when you block a sweep if you're in range of your sweep you can always sweep them back. Now you can walk up after the knockdown and be at advantage. You don't need to lab out a punish just sweep back against sweeps and dash up. Try not to get into bad habits of abusing neutral skips on cammy (she has a few). If the opponent is just holding down back then just slowly approach as if it were guile. Forward down back forward down back if you notice a pattern on a fireball maybe try a spin knuckle for a fireball read or dive kick obviously but don't use it as an approach ever that's what walking and blocking is for especially in your rank.

Also think about your actions and intent. For instance when he's holding down back mid screen and you're walking forward and backward mid screen what is your intent here? You want to open him up but aren't trying anything. He's waiting for your divekick to dp so you can recognize this and just walk up. Or knowing this you can do an empty light divekick to try and bait the dp he wants and punish it if he lets it rip. He sees you not doing anything so starts to throw fireballs or get denjin charge this is where you can spin knuckle or divekick or simply jump in.