If you had drains removed and then developed swelling, it is most likely a seroma or hematoma, although it could be an infection. Both fluid collections require the same treatment options. Infection presents a different set of problems.
I would suggest meeting with your surgeon and let him/her examine you. You may have another seroma, but may have a hematoma or infection. Please do not delay in seeing your surgeon.
This is commonly a seroma. I would recommend a breast US on that side. This could also be a hematoma.
Thank you for your question. If you have unilateral swelling you should consider seeing your surgeon to be evaluated. It can be swelling, a seroma or a hematoma.
You should bring your concerns to the attention of your surgeon. An exam will be important to determine what is happening - seroma vs hematoma vs infection. Seroma may be the most common explanation, but hematomas can occur (rarely) following drain removal, and infections (though also uncommon) can occur with any operation. Appropriate recommendations can then be made if further treatment is necessary.