Is it possible that it is a sinus infection even if my mucus is not discolored all of the time?

Yes: Normally a sinus infection has discolored drainage but clear drainage is also possible. An infection depends on the symptoms over time. Viral and bacterial symptoms are very similar. Even most bacterial infections clear without antibiotics. Consider antibiotics if symptoms worsening after 10-14 days, or persist more than 3-4 weeks. Most virus all infections clear after 10-14 days.