4mo no interest in eating?

My EBF 4 month old baby have no interest in eating during the day, he will latch on, suck for a few seconds, let go, look around, latch again, suck for a few seconds and then unlatched.

He eats at night, and if I black out a room and nurse there he will sometimes eat.

This obviously decreases how much night sleep I get, since he wants to nurse every 2h during the night... and I also feel "locked up" at home until he has eaten, afraid he will get dehydrated..

This has been going on for 4 weeks now and his latest weigh-in was on a lower weight curve than previously.

What can I do to promote daytime nursing? And any other tricks to survive the summer?