If you dog only has the yellow discharge, you could try using over-the-counter eye drops such as Tears Naturale. This helps keep the eyes lubricated and removes any dust or dirt that could cause irritation. You will not be able to get eye ointment with antibiotics without a prescription. Depending on your vet's policy, you might be able a renewal of the previous eye medication without an exam but most vet clinics will recommend that the dog's eyes be checked first.
If your dog keeps her eyes closed or is blinking a lot, this is a sign of pain and should be checked out right away. Painful eyes can be due to a corneal ulcer
and since your dog had this in the past, I would be concerned that it might occur again. Here's some further information about ulcers:
Also check the white portion of her eyeballs. If it looks red, this could be a symptom of glaucoma -- and again, needs a vet exam to diagnose and treat. Here is some specific information about glaucoma in dogs:
Here's a general review of some other things to watch out for:
Use a clean, warmed washcloth to remove the discharge from your dog's eyes as often as necessary.
I hope this has been helpful. If you have further questions, please let me know.