Whoever said that's normal, had a rough time with their baby. My daughter slept 6 or 7 hours straight at 7 weeks.... I was worried I should be going to wake her up to eat the first time she did it at 5 weeks. My husband said "NO WAY, if she's sleeping, you let her sleep!". It was only a few days before the 6/7 hours became normal for her and she is STILL a great sleeper! (at almost 7 years old!)
Try reading "On Becoming Baby Wise".. it is about the order in which your baby eats, plays, and sleeps. Most people play with them, they get cranky so they are given a bottle, then they fall asleep. Wake up semi-happy, play, get cranky, get a bottle (or breast) and go back to sleep... etc... in this cycle. It's backwards. The baby should eat, be kept awake (while his tummy is full and he is satiated) to play, then when he gets a little fussy, put him down for a nap or bedtime. When he wakes, you feed him, then keep him awake and play... THEN down for a nap.
I know it sounds like it doesn't matter.... but... my first one, a boy, was sleeping 6 or 7 hours a night at right about 3 months (10-11 weeks)... my second, a girl, was sleeping much better much sooner than that.
The book is a small paperback that you can read in an afternoon (if you can read AND entertain the 16 month old)....
Just give it a shot... I started it almost as soon as we got home from the hospital with mine, but I would think that your son would adjust to that order of schedule pretty quickly...
I know you are craving some sleep right now.... My son never did nap like some kids did.
When I'd hear stories of my friends 3 yr olds sleeping for 3 hours every afternoon I couldn't believe it! Mine... if he EVER slept more than an hour and a half (naps, not nighttime) it was because he was ill. Usually if I got him down for an hour and ten minutes, I considered naptime a success. He quit them completely around age 3 1/2. My daughter gave hers up early like that too... Some kids are wired differently. But, mine have always slept well at night.
Best of luck to you!