Welcome to the Forum, @kappers - and I am so sorry to hear you are in pain. Yep, definitely get it checked out - I reckon your BC Nurse first (if you have one,) and just contact your surgeon's office as well. Your GP would probably refer you back to them anyway. Your referral should still be valid - tho check, as sometimes the initial referral for specialists is just 3 months.
You should also be seeing one of your specialists (surgeon, Onc & Rad Onc) every 3-4 months in this first couple of years post op - so you will never be 'long' between appointments.
All the best - I hope it settles down soon Take care xx