Since can act as an adverb, preposition or conjunction. You can begin a sentence with since to create an inverted sentence. Place a comma at the end of the phrase begining with since to indicate it is inverted. E. g. , Since it is raining, I am not going out now.
No it is not correct. Since can be used after starting the sentence. For example sentences
like i am working here since last year and our company is in loss since last year.