started talking then stopped?!

Hi all,

Sorry for the long post... My son, when he was 11.5 mos. old, started speaking. He had like 2 new words a day and said them for about 2-3 weeks. We were so excited that he started to talk because his brother was very late to start speaking. Anyhow, after those 2-3 weeks, so when he was about 12 mos old, he stopped using most of those words and started saying other words. I've been very patient and we have always spent lots of time reading, singing and using flash cards and we don't let him watch TV. But now I am starting to worry that almost 4 mos later, at 15 mos. old, he still doesn't use any of those first words... now he uses one nonsense word when he points to just about everything, even for words he know. He now has about 7 words, 4 of which are animal sounds, tractor and yeah for yes. sometimes he will say more and yum-yum also.

Otherwise, all seems to be well. He crawled at 6 mos, walked at 11 and understands my directions and can point out many objects correctly when asked. We also live in a bilingual household. I am just wondering why is he not using those first words and how much longer it will be before his speech takes off again... anyone else had this happen and for so long?? thanks