My butt implant looks so low. Maybe it's too big for my body? Is it a failed butt implant? (photos)

Allow me to answer your question as best i can based upon your photos. However, please keep in mind that an in-person consultation with physical exam is first necessary before any legitimate evaluation or final surgical recommendations can be made. If after physical exam is it it is determined that the implants can be placed deeper and/or they are not currently intramuscular, then a revision to do so is in order. Additionally, if you currently have round implants then a switch to Stanton Anatomic shaped implants  may also significantly improve the overall shape and dips on the side. Glad to be of help. 

A buttock implant revision may be necessary in your case. Be sure to choose a board-certified plastic surgeon that specializes in this procedure and is well known for their work.

No No No ! your implants are fine where they are at; what you are lacking is upper buttocks fullness that can be beautifully achieved on you with VASER lipo of the flank region and transfer to the upper buttocks region. A consultation with a high def lipo provider will really help you appreciate what can be achieved for you.