Running rough, white like substance on oil dipstick

Has been fine last 8mos or so then suddenly went to start
and it was almost dead and had to pump gas to get
started.. Could tell wasnt running same at all and guess
would say seemed less powerful.. Checked oil and creamy
mayo looking substance was all over it, had just changed
oil within one week prior and had never seen this before???
Any ideas on possibilities? We had just put in bit more
coolant which didnt seem to be needed now that look at it
so prob had lil too much, also had been using 10w-30 and
went with 5w-30 for first time bcuz of cold weather... Just
drained oil and it seemed to be as always looked changing
aside from a small amount of this "mayo" substance at
beginning