What Causes Tiredness, Loose Motions And Back Pain While Breast Feeding?

hello doctor Iam a mother of a five months old baby boy. Iam breast feeding him and he is in good health. My problem is that I feel very tired by the end of the day and iam having severe back pain. Since yesterday Iam having loose motions and I vomits twice. Also I donot feel like eating anything. I feel that my neck is slightly swollen in the thyroid region. please give suggest me