I think some peoples hair just grows faster than others (mine grows very fast about half an inch to 3/4 inch a month - my sister in laws grows the same about every 4 months), however if your hair is weak/split it will break off so trimming it keeps it in good condition, use conditioner to avoid tearing hair when brusdhing.
When your pregnant your hair appears to grow thicker because normally you lose about 150 hairs a day and during pregnancy you don't BUT, after the baby you will start losing all the hair you retained - I lost handlefuls ff it. your not going bald just back to normal.