Time and strategy to get back "to form" after illness?

I'm struggling. Went to Mexico almost 3 weeks for a cousin's wedding. Got something. Had a fever the first 5 days, and other GI issues for a total of 10 days. Out of the water a bit over 2 weeks. Lost 9 pounds. It was pretty brutal. I think I actually missed the coffee more than beer or wine! Anyway, finally started recovering last Wednesday, and by Friday I was able to eat a normal meal. I'm still down a little weight, don't know how much is dehydration and how much is muscle/fat mass. Anyway, tried to do a workout yesterday. It was pretty tough. Hackett set, added 5 seconds to each rep (50's). Was able to slog through it, but my stroke count was WAY up, 15-16 and I'm usually 11-12 for this set. Tried again this morning, with strokes in IM order. Ugh. Free was better, but as soon as I did a 50 of fly, it killed me. Cut the set short because I was just plain exhausted. And my fly anyway was horrendous (back and *** were okay). So has anyone dealt with a prolonged virus or other sickness like the flu or whatever that had you down and out for a long period of time? How did you get back into things? There is a new Masters program near me I may go check out (will still be primarily solo swimming), but I don't really want to go until I'm somewhat back in shape. Should I stop doing intervals, and just do some longer, slower paced swims? Should I give it more time? Should I try to do what I did Monday, keep the same distance, but add some extra rest time between reps? Anything diet-wise? I've been just trying to eat a lot in general to get my weight back. Yesterday I added a good deal more protein. Think I may do that, again today.