ad infinitum
again and again
at a stretch
boresomely
boringly
boundlessly
ceaselessly
connectedly
constantly
continually
continuously
cumulatively
cyclically
drearisomely
dully
eternally
everlastingly
fatiguingly
forever
harpingly
illimitably
immeasurably
immensely
in perpetuity
incalculably
incessantly
incomprehensibly
indestructibly
infinitely
innumerably
interminably
irksomely
limitlessly
measurelessly
monotonously
never-endingly
on a stretch
on and on
on end
perdurably
perennially
permanently
perpetually
repetitively
round the clock
steadily
tediously
time without end
tiresomely
to infinity