You may be using needles that are too large for the pattern. You may also be losing track of the increase rows, maybe increasing too many times. It will help if you write out the pattern row by row. Knit one row, purl one row, knit one row, etc. then increase one, knit to last stitch, inc 1 like that. Have you substituted a heavier weight yarn than what's called for in the pattern? This can affect the size and length. Knitters relax after a few rows. The knitting becomes looser than the cast on row. If you knit too loosely, it can affect your initial gauge. It seems like a bother, but it's important to knit a full 4 by 4 inch swatch to measure your gauge, especially if it's with a yarn you're not familiar with.
Is this a multisize pattern? A multisize pattern will say something like cast on 36(40,42) stitches. Increase 0(1,2) stitches, etc. These are for the different sizes in a pattern. When I knit baby things, it would be a newborn, 3-6 months, and a one year size. These are what those brackets refer to. If you see a 0 listed, it means you wouldn't do an increase for that particular size. It's possible you're mixing directions for the various sizes. It helps to print out the pattern and circle each number for your particular size that you're doing so you don't get confused.
What I like about this forum is that people here take the time to answer questions and make comments in a positive way. I've never seen anyone here be mean to another member. This is a safe haven. There are no stupid questions. We've all been brand new knitters at one time so we know how it is. You're not going to know how to do something unless you ask. Welcome to Knitting Help!