I sympathise with this! My father was a shift-worker and often couldn't handle the switches as there was no regular pattern to his rotas.
There is a very very strong human propensity to follow the natural diurnal rhythm of light/awake dark/asleep; if you find it really difficult to buck the biological given don't torture yourself - perhaps you're not cut out for shiftwork and unpredictable sleeping patterns.
If that's not possible to shift your bed to a part of the house where there's no noise of traffic or passers-by, there are several different kinds of EARPLUGS available now (most chemists sell them) and if you can tolerate using them these cut out daytime noises.
Fit good thick LINED CURTAINS on the window of your bedroom, hung well on a curtain-rail (so light doesn't come in at the top).....combined with - if necessary - a draw-down blind. This gives you the equivalent of night-time conditions.
Build up a number of routines associated with sleep. Then, when you do them, you prepare yourself psychologically to 'switch off'. Useful one's I've used when I'm insomniac are sprinkling lavender water on the pillow (or keeping a lavender sachet under your pillow). Lavender has sleep-inducing properties. A drink of camomile tea (acquired taste! tastes foul at first so you have to persist) induces sleep. Buy in teabag form in any large supermarket v. cheaply.
DON'T watch t.v., smoke, drink ordinary tea/coffee, read newspapers or take/make phone-calls for at least half-an-hour before you settle. PREPARE for sleep by starting to screen out stimuli which would not be there if you were sleeping at night.
These 'props' - or others you prepare and set up for yourself before settling down to sleep - set the psychological scene and (literally!) give the brain the message 'it's time to sleep'.
Hope these are helpful!