preposition
1
BAD : I am studying law since 1992.
GOOD : I have been studying law since 1992.
BAD : Since that journey, I never sailed again.
GOOD : Since that journey, I have never sailed again.
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When you talk about an action or situation which began in the past and continues into the present, use a present perfect tense: 'I've been waiting here since 9 o'clock.'
In informal American English, the past tense is also used for this purpose.
See also FOR 4 (↑ for )
2
BAD : I have been living in London since four weeks now.
GOOD : I have been living in London for four weeks now.
BAD : I've been working in a bank since two years ago.
GOOD : I've been working in a bank for (the last) two years.
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since + beginning of period: 'since 3 p.m.'
for + length of period: 'for two and a half hours'
Compare: 'I have been living in London for almost two years, since October 1994.'
3
BAD : Since the last few years, unemployment has been increasing.
GOOD : Over/during the last few years, unemployment has been increasing.
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since + beginning of period: 'I've been living in Paris since July.'
over/during + the period of time within which something happens or develops: 'Over the last eighteen months there have been three tax increases.'
4
BAD : I stayed at your hotel for three nights, since 23rd November to 26th November.
GOOD : I stayed at your hotel for three nights, from 23rd November to 26th November.
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from ... to ... : 'from Monday to Wednesday', 'from 7 a.m. to 3 p.m.', 'from 1947 to 1966'
5
BAD : Bring Eva with you. It's ages since I haven't seen her.
GOOD : Bring Eva with you. It's ages since I (last) saw her.
BAD : It's a long time since I haven't seen you last.
GOOD : It's a long time since I saw you last.
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it's ages/a long time /two weeks (etc) since + past tense (NOT present perfect; WITHOUT not ): 'It's almost a year since I arrived.' 'It must be ages since we last had a meal together.'
6
See SO 2 (↑ so )