Your combo game is lacking. You seem to rely on D-Air for comboing, both on throws and just by itself, too often. When you start a runjump D-Air, the opponent knows (or, at least, SHOULD know) that you're going to end up far forward, so teching toward where you started ends your combo immediately, and if it's shielded, most characters can jump out and hit you easily. If you're getting away with it, that's because people haven't adjusted to the amount of shieldstun, but, rest assured, it's not safe in most cases.
If you're comboing fastfallers, U-Air is almost always a better follow-up for a reliable combo, as you end up right below the opponent and can quickly follow up flexibly. N-Air is also really underrated for combos; it sends people in the perfect position to be D-Tilted or grabbed at lower percents, and comboing N-Air into N-Air isn't difficult to do against most characters, either.
Don't U-Smash unless it's specifically as a KO move or an anti-air, as you can't really combo off of it, it doesn't do that much damage, and it's not as safe as most other options. Get into the habit of using a shuffled F-Air, U-Tilt, or jump-canceled grab (depending on the situation).
You weren't really respecting Sheik/Falco's superior close-range game. Falco can F-Smash for free, and the standard pokes eat Ivysaur alive. Try not to stay in that area unless you've already created an advantageous position with one of your pokes.