Interesting catching up with your latest... I'm not sure what to do about EBT

In the past, if he had a short pm nap, for whatever reason, EBT would work really well for him, he'd get to sleep quickly and be able to catch up on sleep during the night, even doing up to 13h about 6 months ago! Ok more like 12h max more recently, but even so, it worked... Now, he's just taking a real age to get to sleep whenever I PD

All started with us all getting a stomach bug 3 weeks ago when his day and night sleep went bad. He just seems to have got so OT that he can't catch up again. He's always tired, but just can't settle for sleep especially at BT
Now our issue is that his pm nap time has to start between 12:30 and 1pm, and finish no later than 3pm, three days per week, when he's at his childminder's. His previous routine (before it all started going wrong) was:
06:30 Up (if he woke earlier, he'd stay in his cot until this time)
09:30 PD for nap1 (20mins, variable settling time)
1:00 nap2 (2h)
7:45ish BT (ie 4h 45mins A time)
We have occasionally experimented with 1 nap days at the weekend, and seem to find that he needs a first A time of 5h 15mins to get a nap of 2h+ (yesterday it was about 2.5h in total but he needed resettling in the middle, however his previous night's sleep wasn't so good). But we still haven't found the 'right' A to BT with 1 nap, working on that... Once our clocks change (next weekend), I'm hoping for something like:
7:15 WU (can't be later than this for childcare drop-off)
12:30 - 3pm nap
7:30pm?? BT (thinking might need to start out at 4h 30mins A time, perhaps?)
BUT... We've had lots of horrible EWs recently, until yesterday he hasn't managed to get back to sleep at all, but yesterday he went back to sleep at 6:30, just when we'd have got him up anyway! So I tried the above routine, waking him at 7:15 to start the day. Nap was good enough, considering, but it took him ages to settle at BT and then we got 5:30 WU... back to sleep 6:15ish for half an hour only. Tried for a morning nap since I knew we wouldn't be able to give him an early enough pm nap, but that was refused so it was 12:30 PD and only 1.25h nap

He was so tired after that but just could not go back to sleep, we tried for sooooooo long! So, woke 1:45, spend 1h+ trying to get back to sleep and tried for EBT at 6pm... Still trying to go to sleep at 7:10pm, so as you see the EBT just doesn't seem to be working any more

Should I have tried even earlier, do you think? Kara - I agree that OT will always just result in EW, but when you did EBT to avoid this, it doesn't sound like it was actually much earlier than usual? Did you then get EW, or were you able to resettle?
I'm sorry for the mammoth post, I'm just so tired, confused and desperate! I feel like we've got 2-1, 18mo regression and illness (still has a cold which has been going on ever since he recovered from stomach bug) all at once, and I just don't know what to do or how to get any of us enough sleep!