If you're not used to checking your own breasts, then yes, of course you can have lumps that you didn't know were there. As this is the case, your GP is unable to ascertain how long you've had them, if your breasts are lumpy etc etc, so being referred to a breast clinic will give you peace of mind if nothing else.
At a ‘one-stop’ clinic, you’ll see a consultant and have one or more further tests all in the space of a few hours.
To get the most accurate diagnosis of the changes you have experienced, you will have
- A physical breast examination
- A breast imaging test, such as mammogram (breast X-rays) or breast ultrasound scan. Be advised it is quite normal to have both types of imaging.
In some circumstances, they might take a biopsy. This will be done under a local anaesthetic.
As your breasts will be examined quite a bit, be sure to wear a blouse or some other easily removable garment. Separates are easier than a dress/all in one.
It is quite usual for a follow-up appointment to be booked in as you leave. This is usually by phone and takes place a fortnight later.
Lastly, this video is extremely thorough in teaching you how to check yourself. Do so, regularly as that way, you know what is normal for you, and what is not.
PS. Do not panic (and stay away from Google). The overwhelming majority of lumps are benign and absolutely nothing to worry about.