I have a single, deep line under each eye and always look tired! What treatment would you recommend?

It is probably time to address your skin. Bags under the lower eyelids are usually caused by displaced fat, redundant muscle, redundant skin, or sometimes even a prominent vascular plexus giving the aesthetics of lower lid bags or dark circles.
Early volume loss in your upper cheek and tear trough area can exacerbate even a small amount of genetic predisposition to having eye bags. There are numerous, good options to address this issue ranging from nonsurgical to surgical. Which treatment option is best will depend on the underlying cause of the bags
It is important to realize that it is displacement of fat, NOT just excess fat that can cause lower lid bags. Old school blepharoplasty approach took skin and fat out of the lower lids by cutting right through the skin, which gave long term poor results with hollowed out lower lids and more potential for surgical complications. 
We know that we tend to lose fat as we age in our face, so taking more out as part of a surgical procedure may look good immediately, but it is a long term bad idea. Newer surgical approaches to lower lid blepharoplasty do not cut through the skin and leave no external scars, this is called the transconjunctival approach. More important yet, the existing fat is repositioned instead of removed, giving much better long term results with a more conservative surgical technique that also has lower potential for complications. 
Nonsurgical options include strategically placed volume to replace early loss, which can have a dramatic impact on the appearance of eye bags and the junction between your eyelids and cheek. Volume can come in the form of fillers or as micro fat grafting. 
Laser resurfacing can also address these areas when skin changes are the prominent player.To ensure you are receiving the highest level of care, seek out a modernly trained, new-school dermatologic surgeon, oculoplastic surgeon, facial plastic surgeon or plastic surgeon who is board certified and fellowship trained in one of these “core four” cosmetic specialties. Membership in organizations like the American Academy of Facial Plastic and Reconstructive Surgery help to identify a highly trained surgeon. Cameron Chesnut #realself500 Physician 

Thank you for your inquiry.  It appears that the fillers have helped.  In my opinion, your options at this time include manipulation of your existing filler, removal and replacement if necessary, or injection of extremely fine lines of Belotero Balance placed extremely superficially.  The latter option is technically demanding but can produce beautiful results.  Best of luck.

The key is who is doing the injecting.  Not all injectors will be comfortable placing volume in this area.  I recommend that you talk to whoever did your current lower eyelid service and have them place more volume.