Instead of taking expectorant, I would suggest plenty of juice (especially Cranberry) and water over the next three days. 3 days is all it takes for the Nicotine to get flushed out. Here is the link to Joel's Youtube channel. Watch his videos, it may help you.
https://www.youtube.com/channel/UCag4hg_fX_NnOb1N4yXA97Q
Check out the playlist section, and watch the videos a day at a time as organized.
Try to break yourself out of the mentality that this is going to be a non-smoking period. Think of it as ex-smoker freedom. Somehow, in the beginning, your friend has planted the thought that you are a smoker, and that's what set you on a path to smoking and other forms of drug abuse. I don't know how to put it. Here's what I can tell. People have their own way of getting their dopamine release. Some do it through drugs (legal or illegal), some do it through physical activity (my brother told me that there is something called the runner's high), some (like my mom) get their fix by having that cup of tea (or coffee). We are all with you, we all have been addicts, but that's no reason to succumb to junkie thinking and to taking a puff. It is probably difficult for you, but avoid thinking - "90-120 days over, I'm in that haze, now I need to smoke", try thinking - "90-120 days over, I'm not in that haze, time to up the ante on my exercise regimen" (since you like physical exercise). Maybe you could take up yoga with your girlfriend as well, go for the trek. Eat well. All the best!!!