The lump in the neck can be enlarged lymph nodes, which indicate presence of infection in the head & neck region.
Stomach pain can be attributed to either any infection in the Gastrointestinal tract or due to peptic ulcer
Increasing headaches can be due to stress, migraine, sinusitis, etc.
However, presence of all these symptoms can also be due to:
1. Intra abdominal tumors
So, kindly consult a Physician for proper clinical examination.
Investigations like complete blood count
scan of abdomen & lymph node biopsy
will be helpful in clinching the diagnosis.
Wishing your son a Good Health.
Thanks & take care.