Expired Milk

I have my special formula for drinking coffee..
Actually, I'm quite addicted to caffeine..i'll feel quite restless and tired if i don't consume it daily
worse case senerio..i'll have headache if i don't drink..
But! I only do it during school days lar, if i feel tired during normal days..i just sleep lor..

Anw..the yiyi's formula is
1 packet of 3 in 1 coffee powder ( and it cannot be low fat type<--taste like shit)
2 big scoop of milo powder (actually it makes the whole thing taste like mocha..lols)
1 scoop of milk powder ( makes everything all thick and creamy)

So..the cup will be like 1/3 powder._. It's super thick~(for normal people) but i like it lar~
I use fresh milk instead of milk powder if i do have it at that moment
My point is..and i do have one..
i make my usual cup of coffee today..and i realise that it tasted weird..sorta like it sours and it spoils my whole cup of coffee..i dunno what came over me..
I still think it was ok for me to continue drinking it..it smells weird..tasted weird..looked weird
N yet i finished drinking most of it before coming to a conclusion that i should find out what went wrong..it's about 3 hours after my first slip of it...lols..
then i realise that the milk was 3 days expired=.=
i should have realise it when i unscrew that bottle of weird smelling stuff=.=
Anw..i didn't experience any discomfort or what lar..lucky me^^
Maybe i didn't consume it in large proportion lar~