Green’s Dictionary of Slang

bellyache n.

a complaint, a moan, whingeing.

1930		W.R. Burnett Iron Man 9: ‘Now start your belly-ache,’ said Regan.
1938		J. Curtis They Drive by Night 185: [He] was just about as browned off with the old-timer’s reminiscences as he was with Alf’s bellyache.
1947		S. Lewis Kingsblood Royal (2001) 169: This ain’t any sermon that I’m going to give you! It’s a plain bellyache!
1955		D. Niland Shiralee 91: There’d be no belly-aches with that mob.
1959		Mad mag. Sept. 41: Oy Vay Lodge. Formerly Belly Acres. ‘Never a satisfied customer.’.
1999		K. Sampson Powder 142: It was a bellyache in a transit band.

In derivatives

bellyacher (n.)

a whiner, a complainer.

1885		Wichita Dly Eagle 29 Nov. 6/2: To put an easy quietus upon his further complaints, let us say to this dear old belly-acher [etc.].
1893		People’s Voice (Wellington, KS) 14 Apr. 4/2: It’s a cold day when the professional calamity belly-acher cannot find something to make himself miserable over.
1916		Ashland Tidings (OR) 27 Jan. 2/3: There is a guy whose name is The Hellydid [...] and he comes from the River of Doubt [...] He is the original quacker — the original belly-acher.
1925		Portsmouth Eve. News 8 Dec. 8/5: People for the towns are not wanted [in Australia]. Another class not wanted is the ‘perpetual belly-acher’.