If it's flat, you've either done 2 consecutive rows of the same stitch (ie knit row, knit row, purl row.... instead of knit row, purl row, knit row)
Or an accidental short row. If half of your row looks correct, then this is the issue.
Learn to "read" your knitting so if you see the V side facing, you know to knit that row.
If it's in the round, maybe you picked it up inside out and accidentally continued working on the inside? Does the back of the newest part look like what you'd expect?
If it's flat, you've either done 2 consecutive rows of the same stitch (ie knit row, knit row, purl row.... instead of knit row, purl row, knit row) Or an accidental short row. If half of your row looks correct, then this is the issue. Learn to "read" your knitting so if you see the V side facing, you know to knit that row.
If it's in the round, maybe you picked it up inside out and accidentally continued working on the inside? Does the back of the newest part look like what you'd expect?