There has been a major network outage today so that may have had an impact.
As for not connecting at weekends - the more people who try to use a network the slower it gets, networks rely on the fact that not everyone who can use it does so at the same time - for example Tesco is a food distribution network - if everyone who shops at a particular store went there at the same time it wouldn't work, there wouldn't be enough to go around.
At weekends and other peak times the number of people using the network goes up as per my Tesco analogy above - it's called congestion - I suspect your local area is heavily congested and probably won't improve until more capacity is added by O2.
