It's really common for mums to stop feeling a let-down so don't panic. It is often around the 2-4 months mark that breasts 'settle down'. I stopped feeling any letdown at that time and haven't since.
But having said that you've obviously had a big change in her timings. It is possible that by coincidence she is also having a growth spurt.
Or it is possible you are dehyrated as that would affect supply and happens with colds.
I would suggest you drink a LOT and try and rest. I would also suggest you keep a very close eye on how many wet nappies she's having (6 in 24 hrs is a guide) and her general behaviour. If are concerned she's not herself or her nappies are dry then I would talk to your doctor.
I've had some mega colds and breastfeeding has been unaffected - I'm sure you're fine - but keep an eye on the nappies and trust your instincts.
Get Well Soon!