How long until the meds "hit"?

For the past couple of years, I have felt something was wrong. My energy levels had been steadily declining. My TSH/T4 were tested a few times, but everything always showed in normal range.

In February, I had labs done in anticipation of a procedure for a different health concern. I was having some symptoms (that I know now can be thyroid related), but I've had IBS since I was a teen, so I'd just thought I was having a flare; I also deal with anxiety, and I thought maybe the stress of my job was just getting to me. My numbers were:

TSH: 0.1

T4 Free: 18

A couple weeks later, I went back to confirm my results:

TSH: 0.03

T4 Free: 19

My GP referred me to an endo, but didn't start me on any treatment as he said that hyperthyroidism can have several causes and he wanted me to get assessed by a specialist to be sure the course of treatment was most appropriate for my case. Nothing was arranged to keep tabs on my thyroid in the interim.

I finally got in to see the endo in May. He gave me some lab requisitions and said I'd need to go once a month for 3 months to establish a baseline, and that he'd also send me for a thyroid ultrasound, and that after the 3 months we'd discuss treatment options. The next day, I went to get my first round of labs done. My numbers this time were:

TSH: 80.3

T4 Free: 5.9

TSH Receptor Ab: 7.2

Thyroperoxidase Ab: 328

The endo called me back the day he received those latest results and said I needed to start on levothyroxine immediately (no time for an ultrasound). He put me on a 100mcg dose. I've been on the meds now for just over a week.

When can I expect to start feeling better? I feel like my energy levels have started to shift the slightest bit in the last couple of days, but I've been feeling like a shell of myself for months now: back-to-back illness, intense exhaustion, depression/anxiety/mood swings, dry flaky skin like I've never had in my life... It's been awful.

Next labs are scheduled for June 11. Curious to see what those will show.