Thanks for your query.
At 50, the chances of pregnancy
are almost zero.
However, as you are having the symptoms ( and they maybe entirely in your mind, but till you know for sure, you wont feel easy ), please go for a pregnancy test.
As you are not menstruating, then take a pregnancy test 4 weeks after the last unprotected intercourse
Else, once its been a month since the intercourse see a doctor for a blood test
or an ultrasound
dont worry, the odds of a pregnancy resulting at this age, with no cycles, is very low, albeit not impossible.