There's no easy solution.
Well, actually there is - just get out and ride.
You could ride with the slower riders as your recovery rides and do more intense rides as solo ones until you (re-)gain the speed you imply you've lost. Throw in a longer, slower ride to build your endurance and that could also help with your metabolism/weight loss desire.

I'm not a speed demon by any means. But I've gone from slug to acceptable via changing my routine. In my case, I only do one interval session a week because I'm so pain-averse. But I can ride all day long at a slowly increasing pace (compared to a year ago). FWIW, now 58, my mileage for the last 4 years of riding has been <500 (just got into cycling in the late fall), 6500, 1230 (injury-plagued), 2500 (not including a long tour) and 1500(this year, motivation-issue). Things change. Roll with it.