Breast with previous implants are likely to have some scar tissue and seroma, making examining them harder, but not impossible. In general, when lumps change in size, it is generally attributed to hormonal changes associated with menstruation. The area that cannot be moved is likely due to scarring from the implants. Cancers generally grow, sometimes there are periods of indolence, but shrinking and enlarging is an unlikely characteristic. Its probably best to simply continue with monitoring.
A chest X-ray is not likely to “capture” the tumor, the mammogram may. Perhaps the best test is the ultrasound.