I work on one big, ongoing comic and then a bunch of projects on the side - illustrations, one-shot comics and (right now) a pitch for a graphic novel. I'm able to do it because I'm a hermit and a workaholic, and have been drawing comics for well over a decade, so I work pretty fast - but it does sometimes get to be a bit too much, and it's easy to get stuck in feeling anxious about not finishing stuff on time.
If this comic you've just started is your first comic, and you don't have a lot of practise or routine in posting a regular webcomic yet, I suggest you focus on one comic for now, until you get used to it and know how much time it takes to make a page, what it feels like to keep up with updating regularly, etc., etc. Once you know how much one comic demands of you, you might be able to do two at the same time.
In the meantime, scribble those ideas down in a notebook or something, and they'll still be there when you know how you want to deal with them!