I've had my implants for 5 years and I'm 21 weeks pregnant. I can feel a lump. Is this my silicone implant?

It is difficult to determine what exactly the lump is without an in person examination. You should make an appointment with your plastic surgeon immediately. 

This is something that is best evaluated in person.The best way to assess and give true advice would be an in-person exam.Please see a board-certified plastic surgeon that specializes in aesthetic and restorative breast surgery.best of luck!Dr Schwartz

Thank you for your question.  Without a photograph it is difficult to make a recommendation, but your best bet would be to discuss this with your ob/gyn who may be able to identify the cause, or seek out your plastic surgeon directly for reassurance and piece of mind.  Any recent changes in your breast should be evaluated by a medical professional who can help guide you for help if needed.