Gaining too much weight?

i was around 158 lbs when i got pregnant, i had horrible horrible all day sickness and lost about 10 lbs. i am now 23 weeks and just weighed myself out of curiousity and i weigh 164 lbs. is this too much to be gaining? when the books say you should gain 25 lbs is it 25 lbs from the beginning weight or from the lowest you get?