Either do the nolva PCT or dont wait 2-3 weeks before starting the Prop cycle. There wouldn't be a problem with doing a cycle totalling 8 weeks. You'd of course do PCT after that. I'd bump the dose of Prop up a bit though. 350mg/wk is nothing for 4-5 weeks(IMO)and not worth the shutdown that will occur. 25mg of winstrol is rather pointless as well. Triple it for 4 weeks. Better yet would be to forget the winstrol and continue the tren.
I'm not sure why you are using your capability for an erection to determine whether or not you should do PCT after a 3 week cycle that had a fair chance of shutting down natural production. The tren is enough to support your libido while natural T production is shutdown. Or did you mean that you have stopped the Tren for some time now (clarify how long) and are still able to get an erection and feel fine otherwise, referring to the other signs of a normally functioning HPTA.