He only had himself to blame. If he wasn't so undesirable he would have to go to these extreme lengths just to get off. But the ingredients weren't banned and the potion was too novel to be outlawed by the ministry. He would never submit this particular invention of his because the shame.
Severus Snape lived a cruel life. He never had a true lover let alone girlfriend. Before he turned spy for the Order he had to pay to get off. He couldn't do that anymore, tricks would and could sell his sexual fluids to biggest paying death eater. Hence, this potion that was purple rain purple that was his solution to his problem.
Severus was in bed when he took the potion. There was pain when his body split into his feminine doppelganger but it was short lived. As he looked into her eyes, he knew this night would be fruitful for him until she disappeared like a cloud on clear day. Well at least he would get some self loving tonight.