I'm now a 38DD and I have neck and back pain. Also sagging breasts. Would you recommend a lift or a reduction?

Thank you for the question. Based on your description, you may be an excellent candidate for breast reduction surgery.  Breast reduction surgery will “automatically” serve to lift the breasts; improvement in any breast symmetry would also be a goal/byproduct of this operation. However, much more information is needed to determine whether you should proceed with surgery, and if so when (timing).  In my practice, I individualize the “timing” of surgery based on a lot of information that is transmitted during the consultation process.
“Typical” patients who present for breast reduction surgery are women who have disproportionately large breasts, causing problems such as neck/back/shoulder discomfort, postural changes, bra strap grooving, skin irritation/rashes under the breasts, and/or difficulty with activities of daily living and/or exercise etc. There may be both physical as well as psychosocial “stress” caused by the disproportionately large breasts.
Reducing breast tissue mass and elevating the breasts on the chest wall tend to improve or alleviate many of the symptoms associated with the disproportionately large breasts.
Patients considering breast reduction surgery should also consider the potential downsides (risks/complications) associated with the procedure as well. Poor scarring, for example may be associated with the procedure.  Additional surgery may be necessary in the short or longer term for a multitude of reasons.
When the time is right, I suggest that you seek consultation with well experienced Board certified plastic surgeons who can demonstrate significant experience achieving the types of outcomes you would be pleased with.
Then, I would suggest you visit a few surgeons whose practices concentrate on aesthetic surgery. Ask to see lots of examples of their work and preferably speak/see patients who have had similar procedures done.
I hope this, and the attached link (dedicated to breast reduction surgery concerns), helps.  Best wishes.

You may be a good candidate for a breast reduction. Best to be seen in person to determine what would be right for you.