Paul, in his first letter to the Thessalonians, said that "the Day of the Lord" ARRIVES "exactly like [hosper]" the INITIAL "birth PANG [SINGULAR]" that comes upon a woman (the very SAME word that Jesus used in the plural when referencing the "PANGS" ['beginning of'])... which is what Jesus had already talked about in Matt24:4 / Mk13:5 "A CERTAIN ONE [(bringing deception); 'A CERTAIN ONE [G5100 - tis]'] (which is the FIRST/INITIAL one of THOSE "birth pangS" Jesus spoke of).
How you had written it (in past posts) is that Paul was saying "birth PANGS [PLURAL]," but he actually said "birth PANG [SINGULAR]" (1Th5:1-3, where speaking of the Day of the Lord's ARRIVAL point in time). IOW, it does NOT commence at the MIDDLE or END of the Trib years, but at its START.
Once this is acknowledged (from the text itself), one can then place things in their proper time-slot [/chronology].
Many people mistake this, thus come to incorrect conclusions as to Paul's actual point(s).