I am worried about this bump on my forehead. The more weight I gain the bigger it gets. I've had it for 3 years now. (Photo)

Lipomas are benign fatty tumors that occur underneath the
skin. Most lipomas require surgical removal once they are bothersome. It is
important to make sure that the growth is not something else before assuming it
is a lipoma. There are many other subcutaneous nodules that mimic lipomas in
shape and size. Surgical removal of lipomas is relatively straightforward and
requires meticulous attention to detail. The first stage in improving your condition would be to
schedule a consultation to discuss your options after a complete examination is
made. Raffy Karamanoukian MD FACS

This is most likely a lipoma, which is a benign fatty tumor. These lesions are relatively easy to remove surgically.

This is most likely a harmless fatty growth called a lipoma, but to be sure you should be examined in person by a dermatologist in your area. Best, Dr. Groff

You would need to be examined to try and determine what the lump on your forehead is.  The most likely causes would be either a lipoma (if it is soft) or bone (if it is hard).  There are surgical treatment options for either cause.  I would consult with a facial plastic surgeon or plastic surgeon to be evaluated.  

Without an exam to feel the mass, it is impossible to make an accurate
diagnosis, but based on your description it is most likely a lipoma (a benign fatty tumor). The treatment is excision. The incision
could be made in a natural forehead crease for optimal scar camouflage
and would likely be smaller than the mass itself. Another option is to
make an incision at the hairline and excise the mass from up there. Be
sure you see a facial plastic surgeon or plastic surgeon. I wish you
well!