I have had a small breast cyst in one of my breasts for years. It was a bit smaller than a small olive, but I had biannual mammos and ultrasounds for years to make sure it was stable. This is the first year I've had a mammo only once (since it appeared to be so stable). I woke up one morning this week to find it was huge... the size of the top of a soda can. It still feels oblong, but with an additional, smaller bump on top. It's very hard. Not squishy at all. It also doesn't hurt. Recently, I had xrays to make sure I didn't have pneumonia. Also, my dose of synthroid increased due to rising TSH levels, and I started the birth control pill about 4 months ago. Could my cyst have become cancerous? Could cancer just pop up so quickly... undetectable one day and huge the next? On the other hand, if it is just a cyst, could any of the recent occurances/changes in my life caused the cyst to grow? I'm 45.
It sounds like you have done a good job of being aware of breast changes and getting them checked out. Cysts can change in size dramatically, and the birth control pills could be a factor because hormonal changes can affect cysts. I had one increase dramatically overnight once for no apparent reason. The surgeon drained it, and it was fine. One problem with cysts is that they can hide solid lumps that may be cancerous. Although the sudden change in size of the cyst is probably nothing to worry about since you've had it checked out before, it is a change you should discuss with your doctor. The small lump you are feeling on top of the cyst definitely needs to be checked out by the doctor. It will probably be fine, but do call and find out for sure.
Even though this is a cyst that you are familair with, and have monitored over time - I still think that you should have it checked out just because there has been changes - and only an ultrasound, mammogram or other diagnostic tool can say for sure what these lumps are or why the change in size.
Especially contact your doctor if these changes last for more than 2 weeks or if either lump gets bigger.