How do we use this, in sentences such as:
'Since coming here, I have learnt a lot of spanish'
'It is 2 weeks since i last had a day off work'
'We've been here since Monday'
Using it before a conjugated verb, as in the first example, is there any subjunctive involved?
Thanks.
Yes, although ya que or desde could be used (although in some different contexts). And I think (again, I'm not an expert) this would be a good translation.
i would agree that those make the most sense. FOr the first one you changed it to 'since i came here' , which is a good way around the problem .
Would the last sentence translate as 'hemos estado aqui desde entonces lunes' ?
I assume in Spanish for 'since' the phrase 'since then' is used all the time?
Cheers 
Desde entonces vine aqui, he aprendido mucho español.
Ha habido dos semanas desde entonces mi último día de vacaciones.
I'm not sure of these, but they are correct to the best of my knowledge.
Thanks - can you offer any translation help for the examples shown'
I don't think the subjunctive would be used, as there isn't any doubt about you coming here. Since just indicates a period of time has past since (no pun intended) the event reffered.