Toddler sleep problems

I have a 15-month old son who wakes up repeatedly throughout the night asking to be breastfed (3 to 4 times per night). He usually sleeps at least 4 or 5 hours in the beginning of the night (sometimes more) but then wakes up every 1 to 2 hours until morning. Sometimes, I can get him to stop crying and go back to sleep earlier in the night by cuddling him. However, later in the night/in the early morning he will only stop crying and go back to sleep if he is breastfed. Ever since he was born, he has had trouble going to sleep and staying asleep on his own. His naps tend to be short (1 to 1.5 hours with 1 nap only per day). He does not seem to be in pain (even when teething) and does not seem scared when he wakes up.

We just started putting him to sleep in a sleep sack because he kicks the covers off when he is sleeping. He is very active and agile (can climb almost anything). He talks a lot and has a large vocabulary for his age (close to 100 words at 15 months). He is usually a little reserved when he first meets someone or first arrives somewhere, but once he is comfortable he smiles and chats a lot. He loves to dance, move around and go outside. When he is tired, hungry or in a new place, he wants to be held and will cry if I do not pick him up immediately. Otherwise, he can play by himself and is not too clingy.

He sometimes gets very tiny pimples on his face (they are the color of his skin - not white or red) but almost never gets diaper rash. He hates eggs but seems to like everything else (particularly tomatoes, sweet fruit, chicken and avocado). Overall, he has a good appetite and is quite healthy. He has tan skin, dark hair and eyes, is slim and average to tall for his age, and has a slightly larger than average head.