Hello from JustAnswer.
Nausea is a side effect that can occur from virtually every antibiotic, including Keflex, but it is generally not an allergic reaction, so is not a side effect that would indicate a need to suddenly stop the Keflex. If the nausea is severe, particularly if it is associated with significant vomiting, then it may be necessary to stop the Keflex. But if the nausea can be controlled or significantly eased, then it would be fine to complete the course of the Keflex.
The better medicines for nausea are only available by prescription, but there are some home interventions that can be tried. The Pepto-Bismol is fine to take, although it apparently did not help you very much. There are certain antihistamines that have a mild effect to help ease nausea. The best available over the counter are primarily marketed for motion sickness, such as meclizine or dimenhydrinate (e.g., Dramamine or Dramamine II). Benadryl/diphenhydramine also may help. It may not be as good as the meclizine or dimenhydrinate, but it has the advantage that there is a good chance that you may already have some in your medicine cabinet. It also can help to be drinking some clear liquids, such as fruit juices or sports drinks. Carbonated beverages can be soothing for some people, but the carbonation may make nausea or vomiting worse in others. Some easily digested foods, such as saltine crackers, may also ease nausea.
If these home interventions adequately ease the nausea, then it would be fine to continue the Keflex. If necessary, your doctor can provide a stronger medicine for nausea, once you can contact your doctor tomorrow.
If I can provide any additional information, please let me know.