Yes, there is expiry date for the medicine.
If you know of a vet that is reasonably priced, you should bring your kitten there for check up.

Involuntary discharges aren't normal, and we really can't tell what could be the problem.
My suggestion is to go see a vet asap.

Spaying the cats definitely helps with the overpopulation of cats

As for feeding the strays, lots of people have very strong feelings about that, I have certainly heard a lot of argument about why we shouldn't feed the strays.
I feed strays at my area, but my area has basic cleaning for hallways and stairs, and I seldom see animals dirtied the properties.

I am not too sure about sending the kittens to shelter though.
Many shelters kill animals that is not adopted within certain time, I am not comfortable about doing that.

Several no-kill shelters that I know of, is so overwhelmed and I am not sure they can cope with extra animals.