I have been on Propecia for 6 months and have seen no benefit at all, not even a slowdown in the amount that I lose daily.
Can we really expect to see positive results on Propecia if we’ve seen nothing after 6 months?

Any changes in the process of hair loss or gain are subtle because of the gradual nature of hair growth. The medication Propecia (finasteride) affects patients differently. For instance, patients in their 20s may have a better response to Propecia than a person in their 50s. The drug seems to work better in recent balding, so young men who are earlier in the hair loss cycle get better benefits (as a rule). I always check the miniaturization of the entire scalp before starting my patients on Propecia and follow my patients over 12 months after starting the medication for assessment of their gain or loss. In your case, if you had a prior examination, it is a good time to get checked again for comparison. If not, map your miniaturization now to at least get a point of reference for future follow-ups.
I would generally not give up on Propecia until after 12 months of treatment. The effects in some people are very subtle.

Demodex folliculorum is a tiny mite, less than 0.4 mm long, that lives in pores and hair follicles. It is usually seen on the nose, forehead, cheek, and chin, and often in the roots of your eyelashes. Demodicids look like worms. People with oily skin, or those who use cosmetics heavily and don’t wash thoroughly have the heaviest infestations, but it is not uncommon for adults to carry a few demodicids.
Some people can have some side effects of drugs that are used for sedation after a hair transplant. Every medication has side effects, but most of the medications we use have few detectable side effects at the doses we utilize. If there are any lingering effects from these drugs, they may last a day or two at most. There has been a rare occasion where a patient was recently sick with the flu just before a transplant, so it would be logical that the same thing could happen after a hair transplant. Perhaps he caught the flu and it was coincidence. I really can’t tell you, as I have no idea.