Is there a link between the change in dosage of sertraline and my difficulty in achieving orgasm?

It is indeed possible that this is a side effect of sertraline and it is often dose-related. Unfortunately, this type of side effect is not always habit-forming. There are some solutions. For example, the dose of Sertraline can be reduced and another medication can be added to counteract the side effect, e.g., wellbutrin or remeron, if this is appropriate for you. Otherwise, some molecules in the anti-depressant class are less likely to cause this problem, e.g. trintellix, but this product is only covered by some private insurances. Hopefully this answers your question!