Am I irritating or does he really not use facebook often?

[Rose]

There's this guy in my uni course who I've only spoken to a few times about a group assignment we were doing. We've been away on prac for the last four weeks so I decided to add and message him on fb asking how things were going. We've messaged a couple of times over a period of days but the last message I sent was on saturday and I saw that he only looked at it last night. He has mentioned to me that he isnt a frequent user of facebook- and I can see that from his wall- but he hasn't replied to my message yet...
am I reading too much into it? could he just have not had the time to reply?- I know I sometimes take a while to reply... I don't think I'm being annoying... it's not like I have been asking alot of questions in my messages- the last one just had two, and they were spaced out...

help.