I am breastfeeding 1, 5 month old baby. At night have overabundant milk but during a daytime I dont have much (and feel let down just few times).

Not sure Iunderstand. I think I am understanding that you don't have let-down at night. I quick call to your local hospital OB department can put you into contact with a lactation specialist. These specialists won't mind getting the full story and making suggestions-for free!