My cat's head is twitching and sneezing a little. Is she sick?

I've had my shelter cat for almost 6 months and she'll be almost 2 years old. I've been on a trip for a week but have checked in with my cat and just today, I noticed that she has been sneezing alittle (more than usual, but not alot to deem "sick.") and when she is awake and sleeping, she'll twitch her head and sometimes one of her front legs. I have no idea how long it has been going on and she has never done the twitching before. She's still active but alittle less than normal. She is still eating, drinking and using the litter normally. When I first got her she had an upper respiratory infection in the past but went away on its own. My carpet was cleaned 5 days ago so maybe she's allergic? Is she sick? Is it serious? I read online that maybe she has fleas? (She had tapeworms when I first adopted her) which may be why she is twitching her head and cleaning often, So I put some flea medicine on her. Should I monitor it for a couple days? Should I see the vet ASAP? Is she sick? I apologize for the detailed, complicated question but I'm worried out of my mind!! Please help!! I don't want to lose my little girl!