The best mucolytic (mucus thinner) I have found is 10% acetylcysteine (for which I use a nebulizer). It stopped a long-standing congestion problem immediately.
You say you had a lot of tonsil problems -- did they put you on antibiotics a lot? If so, it killed off your beneficial flora that live in your intestinal tract and elsewhere, causing your immune system to suffer. Try taking a good probiotic in the refrigerated section of your best local health food store. You should also examine your diet for allergenic foods -- the most common culprits are wheat and dairy, but many other foods can cause problems as well, including soy, corn, and others. Other foods are pro-inflammatory, such as sugar and highly processed flours. There are many natural antihistamines that might help, including freeze dried nettles, Chinese skullcap (scutellaria), combinations of bromelain, quercitin and Vitamin C, and many others. You might want to buy a book called Prescription for Nutritional Healing and its companion Prescription for Herbal Healing for some ideas here. You can also work on your immune system, either to tamp it down or ramp it up, whichever is most appropriate. Perhaps seeing a naturopath would help if you don't know your natural medicine. Good luck.