Does One Build Up a Tolerance?

[Julios]

I have been prescribed Trimix by my uro with the following compound:
20MCG/ML Alprostadil,1MG/ML Phentolamine, 30MG/ML Papaverine
I was to start with 0.1 ml, and increase the dosage if needed by 0.05ml increments seperated by at least 24 hours, until the dosage was sufficient for achieving a good erection.

With 0.1 I got a great hard on that lasted 80 minutes, but it was painful. Two days later I reduced to 0.8 and got as good a one with way less pain. A couple days later went to 0.6 and got 95% for about 30 minutes and no pain. A couple days later went to 0.7 and got only 50% for about 15 minutes.

Am I building a tolerance? Has anyone else noticed this? If so, please provide the following:
- compound
- initial dosage to provide 100% erection
- dosage used now to achieve 100%
- duration since starting injections

Thank you