vaginapagina | Mid cycle spotting

Hi!

DH and I have been TTC since June (didn't prevent for early June cycle or early July cycle and actively tried for late July cycle using FAM and OPKs). I know our sex was perfectly timed in late July, but my period came right on time.

A bit about my cycles and me:
29y, very regular periods
Cycles are 25-27 days long
10-12 day luteal phase
No HBC used in the last five years (copper IUD removed May 2015)

I do not have a thyroid, but my hormones are pretty well balanced on 150mg of levothyroxine 6x per week, and 300mg on Mondays (TSH at last check: 2.06, free t4: 27).

Since June, I've been having spotting (brown to red) about one week before my period (usually like 7DPO). The spotting typically intensifies after sex or a bowel movement but does not require a pad. It always lasts for three days, then stops. I keep hoping its implantation bleeding but that hasn't been the case yet.

Should I be concerned about the early spotting and short-ish luteal phase? I'm concerned it's maybe luteal phase defect or something. I'm probably overthinking, I know in healthy couples it takes usually at least three or more cycles to conceive, I'm just feeling impatient.