Recommendations
You will need about several recommendations from professors - normally ~2 science professors and ~2 non-science professors - and the rest can be from bosses in college, coaches, supervisors, advisers, etc. Make sure you get recommendations from professors that respect you; you may earn their respect by performing well in their class.
Those doctors you shadowed are able to write "personal" recommendations that you may need when applying to specific schools.
--Depending on what university you're applying from, your school may offer the option of a committee letter. This is a letter that takes multiple evaluations from various professors (~7+), and is converted into one letter by the professor of your choosing. This letter is then signed by all people whose marks were mentioned. This letter supplements needing multiple recommendations from professors. Ask your pre-med adviser if your school offers this, mine did.--