Problem with multiple observations from the same individual and time between admissions.

Dear friends,

I am working on a project concerning intensive care. I have a dataset with 4993 observations with unique patients ID. Our software for intensive care creates a new patients ID each time a patient is admitted to our intensive care unit. For that reason, each patient can have multiple patients ID, but obviously the same social security number. My goal is to calculate number of readmissions using patients ID, social security number, admission time and discharge time.
My variables are:
Array

In short, I would be extremely grateful for advice on how to:
1. Create a new variable named "No. of Admissions" based on SocSecurity and PatientID for each SocSecurtiy (i.e. for each SocSecurity: 1, 2, 3...admissions
2. Calculate time between "DischargeTime" from first admission to "AdmissionTime" for second admission (and in relevant cases, between second and third and so on)

Array

I myself and also the rest of my research group have just recently started using STATA. I therefore don´t know if this is a big question or not. Please bare with me.

I am using Stata/SE 14.2 for Mac (64-bit Intel

Very grateful for advice, and also please let me know if this question is totally out of order.

Regards,

Erik Zettersten, MD Anesthesiology and Intensive Care, Karolinska University Hospital, Stockholm, Sweden