A patient is identified by a patient id. A patient has name, date of birth, allergies, and weight recorded as part of the patient record.
A physician is assigned a physician id. Physician name and expertise need to be recorded.
Patients can possibly visit the hospital multiple times. Each time a patient visits the hospital, they receive a visit id. For each visit, the admit date when the patient arrives and the discharge date when the patient is released are recorded also. The diagnosis for the reason of the visit needs to be recorded. When a patient visits the hospital, s/he is always assigned an admitting physician.
During each visit, a patient may receive multiple treatments. Each treatment is administered by a physician. When a treatment occurs, the date/time, treatment code, and physician notes all need to be recorded.
Patients receive drug therapies during their visits. Each drug therapy is identified by a therapy id. The date/time the drug therapy was administered, information about the dose, and whether the drug therapy is active need to be recorded. A patient typically has multiple drug therapies during each visit. A given therapy event may include more than one drug.
Drug information is recorded in a hospital formulary (master list of medicines that might be prescribed). Drug information includes a drug id (identifier), drug name, drug type, cost per dose, and price per dose. A specific drug therapy could require multiple drugs (think of an IV composed of several drugs).
During the visit, patient vital signs also need to be taken and recorded. The Vital id, date and time it is performed, type of vital (such as Blood pressure, Pulse, Temperature, Respirations and O2 Saturation %, etc.) and the result readings need to be recorded. Vital signs are usually recorded multiple times for each visit. Take an ICU patient as an example, their vital signs are taken as often as every few minutes.
If information provided is insufficient for a decision (e.g. determining the cardinality of a relationship), you can make reasonable assumptions. However, your assumptions must 1) not contradict information provided and 2) should be clearly noted on your models for your reference. You may add a simple key (e.g. customerID) to an entity if there is not a clear choice of an existing attribute that should serve as a primary key.
Creating this models will help answering further questions