It's quite possible that this could be primarily a physical issue but there is most likely an emotional component to it. Have you had your thyroid level checked? Hyperthyroidism can lead to inability to gain weight.
So keeping all of that in mind, yes, acupuncture can be helpful if you are willing to be open and honest with your acupuncturist and take their suggestions. Together you can figure out the underlying causes and conditions and hopefully resolve your problem. Good luck!!
Lifestyle choices such as poor eating habits, not getting enough sleep, improper hygiene, obesity, stress, etc. are in large part to blame. Some forms of the flu or viruses out there nowadays are quite virulent and even if you do take extra good care of yourself, you still may get sick. But one is less likely if you eat plenty of fruits and vegetables (vitamin C among many other helpful nutrients that promote immune system health), get enough and regular sleep, avoid stress, exercise regularly and so on. Chinese medicine recommends eating well cooked vegetables in the winter time. It aids in digestion and keeps you in tune with the natural rhythms of the body's cycles.
If wash your hands frequently in the winter that's great, but using good quality hand moisturizer is key to avoid skin breaks where viruses can sneak in. I personally think a lot of people spread germs through door handles. So use a glove or your sleeve when opening doors. Good luck and good health!!!
All this aside, even if you are getting acupuncture, there is no guarantee that you will not fall victim to the common cold or flu. Even those of us who are chronic hand washers, health nuts and long-sleepers can still be vulnerable to the many strains of viruses out there. But those that get proper rest, exercise and diet and practice stress reduction techniques have a greater chance of keeping colds at bay.
Diet, sleep and exercise play a HUGE part in how your body responds to the condition as well. Seeing a dietician and seeking advice from your doctor as to how much sleep and exercise are recommended for you may be a good idea. Environmental factors such as humidity, living in a damp or moldy environment, excessive heat or cold can affect fibromyalgia pain. Of course, I'm sure you already know a lot of this. But doing further research on how to help yourself will only aid in your recovery and help decide if acupuncture is right for you.
Acupuncture needling and other modalities such as cupping, magnet therapy, gua sha, massage and so on can be very helpful. But the degree to which they help can vary from person to person. Needles may be too traumatic for some to handle. I have done acupressure on patients that are too needle phobic. That's massage in a specific therapeutic way on the points where I would have placed needles. The comfort of my patients is of the utmost importance and if needling causes severe pain or anxiety, then that is counterproductive to treatment. It's normal to feel a little pinch, or tug, people describe it in different ways. But it should go away within a minute and if it doesn't, or it gets worse, I take it out. There are other points that I can try.
I also would highly advise you to try some relaxation techniques such as yoga, meditation, tai chi, etc. These can help with sympathetic and parasympathetic responses to pain as well. Good luck!!!
That being said, yes, acupuncture can help balance the system but there are a lot of things that you can do on your own to combat stress. Join a stress reduction support group. Practice tai chi/yoga/meditation. Really think about what makes you feel relaxed and do it often. Visit a pet shelter (if you like animals) and experience the relaxation and happiness that comes from holding a purring kitty!! Playing with kittens always works for me!!!
A lot of the stress in your life is truly in your hands to do something about! Thanks for writing and good luck!!!