Present perfect/past simple with "over the past months/years etc"

Question

I have been following a diet over the past months but I haven't lost any weight. I have tried everything but nothing has worked. A couple of times I thought about giving up and I was about to quit but I never gave in to that tempation

Is what I have written well-written from the grammatical point of view?
Should I say "I have never given in to temptation" instead?

Sometimes I have trouble understanding when to stop using present perfect and use past simple when using expressions such as "Over the past months" and similar.

Answer 1

I think the present perfect is fine there. Over the past months does not exclude the present. The present is a part of that time span.

You are correct to switch to simple past with "A couple of times I thought..." since you're referring to things that took place in the past.

You could continue that sentence in simple past "... but I never gave in" or you could revert to present perfect "... but I have never given in". It is your choice. Present perfect would bring us back to your present state of being someone who has not given in to temptation. Past would refer to your not giving in when those temptations presented themselves.

Answer 2

This sequence of sentences is fine. It's an excellent example of using the present perfect to transition between your present state and your past actions—and leaving an 'anchor' in the present to transition back and continue with (for instance) an account of what you intend to do next.

You may find this of value: §4. When and how should I use the perfect? of our canonical post on perfect constructions. But you seem to have a pretty good grasp of use already.