I’m looking to do some home improvements like adding a few circuits in my house. I’m putting a light and a outlet in my garage which is 20ft’ away from my house and I’m putting two outlet in my office and in a few months I’ll be adding a second bathroom. Which will have a light or two and an outlet. What I want to know is should I upgrade my AMPS? I now have 100A service.

add your breakers up (5-15amp=75, 2-20amp=40 70+40=110) if yours adds up to 150 get 150 amp service

Adding the breaker ratings is not how a service rating is calculated. Services are sized according to the various allowances and demand factors found in Article 220 of the National Electric Code, and illustrated in the Examples in the Annex. How to review the code is in the Read First sticky post.

Specifically Section 220.31 is for adding load to an existing service.

Without getting into the details, your proposed load is minimal and a service change should not be necessary.