Hi
Welcome to the MedHelp forum!
It is difficult to comment without examination. Lump behind the ear could be an abscess, folliculitis (hair follicle infection), lipoma (localized collection of fat), a cyst, an inflamed lymph node or a neurofibroma (localized harmless swelling in of nerve and connective tissue). You may not have been sick but local infections like dandruff or a dermatitis too can cause a lymph node to swell and be tender. However swollen lymphnodes behind your ears could be due to chest infection, tonsillitis or pharyngitis, dandruff, infection of ear or even metastasis from a cancer. It could also be of tubercular pathology. A fine needle biopsy or a CT scan of the swelling is only confirmatory.
Regarding stomach pains, it could be acidity, gall bladder problem, gastric reflux, fibroids, ovarian cysts etc depending on the location. A CT scan of the abdomen should be done. If it is due to acidity and reflux, then this can also cause headaches. Taking omeprazole and antacids may help.
It is difficult to comment beyond this at this stage. Do consult your doctor.
Hope this helps. Take care!
you know some food allergies can cause stomach pain like that not all allergic reactions will cause you to break out some will cause stomach upset and severe stomach pain my sister suffered 5 years before they figured that out start keep a food journal note what you eat every time you have this problem pain then go to your doctor and ask them to test you for allergies to that food