I have 42H breasts but should be wearing a size J according to fittings. I need help badly.

It sounds like you would do very well to consider a breast reduction surgery.  Be sure to discuss your goals and concerns with your board certified plastic surgeon and consider the pros and the cons. Be certain your surgeon is properly certified.  I've attached a link where you can start your search. 

Thank you for your question, I strongly recommend you consider a larger cup size as going too small may jeopardize vascularity and wound healing. Women no longer need to undergo massive breast reduction in order to experience pain relief. Please consider The Horndeski Method/The Bellesoma Method to alleviate pain from large breasts by transfering the weight of breast to the underlying chest muscles. This maneuver relieves the skin envelope in being the only structure holding breasts in place. The muscle acts as an active structure that easily maintains and lifts breasts long term. Attached is an example of a woman who wanted a lift without implants and without the ugly vertical incision. You are welcome to visit my gallery to see more examples. Best wishes, Dr. Gary Horndeski

I'm sorry to hear about the problems your disproportionately large breasts are causing you. 
Based on your description and pictures you may be an excellent candidate for breast reduction surgery.  “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 would suggest starting with the American Society of Plastic Surgery and/or the Aesthetic Society of Plastic Surgery to obtain a list of well experienced board-certified plastic surgeons.
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.Before undergoing the breast reduction procedure it will be very important to communicate your size goals with your surgeon.  Most patients wish to achieve  enough of a reduction to help with their symptoms while remaining proportionate with the remainder of their torso. 
With the goal of improving communication with my patients I find the use of photographs of “goal” pictures (and breasts that are too big or too small)  very helpful. For example, I have found that the use of words such as “proportionate” or “C or D cup”  means different things to different people and therefore prove unhelpful. Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup size may also be inaccurate.
I hope this, and the attached link, helps.