Lump under my arm

Hi, welcome to the ehealth forum and I am glad to help you.
If the size of lymph node (lump) has decreased it shows that it was reactive in nature and with the healing of infection, the size has come down. It happens to be reassuring. With antigenic exposure, lymphoid tissue increases in volume so that the cervical, axillary, and inguinal nodes are often palpable during childhood. But palpable axillary lymph node as in your case are not considered enlarged unless the size is greater than 1 cm. So, if the persistent size of lump in your case is less than 1 cm, there probably is no alarm.
Your BMI calculates to about 25 which is uppermost limit of normal. Anything above 25 falls in overweight range. You can adopt a healthy lifestyle and start healthy diet and healthy exercise regimen to control the weight from increasing in consultation with nutritionist and fitness expert.
Hope this helps. Take care.
Note: This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.