Do I need to see a therapist if I have extreme guilt?

If you were to see a therapist, you could ask about whether or not you need therapy. Obsessing over little things can be a sign of depression. You can take a depression screening test online, such as CESD R. There's a variety of things that can help with depression. I have details in my answers and you're welcome to click and read. There are things that help if you have a mild problem with your moods, not bad enough to be diagnosed as a mood disorder.

Treatment usually begins by seeing the GP, who can give you a referral. I mention referral because just a bottle of pills is not a very good approach. The things you'd want to tell the doctor are how you feel at different times of day, any symptoms you might have such as change in appetite or sleep, and things in your life affecting how you feel.