My sons swollen penis, do I need to be concerned?

The past few days my son has had horrible, liquid diarrhea. It’s been terrible! Anyways I was changing him today and my 8 year old nephew (who was standing there talking to me) pointed out that near the tip of my sons penis has a “big bump” on it, had he not pointed it out I probably would’ve never noticed because I generally just try to make the diaper change quick and easy since he looooves to fight me (he’s two and hates being slowed down) anyways, I asked my mom because she’s had her fair share of children and grandchildren so she knows quite a bit, she said it could be from where he’s had diarrhea, that maybe it had just bothered his penis and that’s why it’s swollen near the top, and from the smell of his poop (that probably sounds weird) I’m almost positive he’s cutting teeth (his poop smells different depending on what’s going on with his body) because he has also quit eating a whole lot and just hasn’t felt so good the past few days. I was just wondering if this could be a possibility? Because he’s had the diarrhea constantly and it has made a little rash on his butt, I’m trying to see if it’s that serious, because honestly I’m freaking out, which I tend to do a lot when it comes to my kid and sometimes over nothing big.