Should I get a second hair transplant to fill in temples? Disappointed with results so far at 5 months

The results from the initial transplant can take up to one year to completely show the effect on the scalp. There is no right or wrong age for a hair transplant or to determine the area of transplant, the symptoms and grading of thinning and balding are what truly matters.
Nevertheless, if the patient is unhappy with their results, they can always opt for a second transplant to enhance their appearance and fill in the thinning or balding parts. A hair transplant can also be successfully used to lower the hairline which can be of great benefit to patients with male pattern baldness.
As for the price, many reputed clinics across the world may be more pocket-friendly.

FUE hair transplant can be an option for correcting receding hair line on temples and asymmetry on your frontal hair line/forelock. I advice you have a FUE with 1800-2000 grafts; you would achieve the desired hairline in just one session of dense packing hair transplant.

At 5 months post op it is too early to see results. Before and afters are taken at 1 year to see the results.

First of all it is unclear how your before situation was.Also, you may want to discuss as to how your hairline was drawn. Was it a quick one stroke line, or was it discussed in depth before the treatment?
As for your regime you should give the medication more time, 5 months is too short.Typically 10-18 months is what it takes to stabilize your hair loss.
However if you want to know if you are responding to finasteride and minoxidil you could perform a special hair DNA test which is now available.