Since का use conjunction में 'से' या 'के बाद' की तरह किया जाता है.
Sentence में SINCE से पहले वाला verb present perfect tense में होना चाहिए और उसके बाद वाला verb past indefinite tense में होना चाहिए। Example-
Incorrect- Many rules changes since I had left.
Correct- Many rules have changed since I left.
Incorrect- A week passed since I have been contacting you.
Correct- A week has passed since I tried to contact you.