One thing. You started training in the colder months, and we have had unseasonal warmer weather on and off in the past month.
I find that my body takes time to adapt to the warmer temps. So when it is April and warm, its v hard to run in warm weather. But, as the months go by, the body slowly adapts to the warmer weather, and it does get better. Come July, yes I do find it hard, but it is easier than when it was April.
Just stay with is, allow yourself to go a little slower when its warmer, and your body should get used to running in warm. Good luck!
My HRM strap went once, and I tried to change the battery to no avail, I still would not pick up a signal.. I took advice for the net/ RW forum, and it said to put the battery upside down from its normal position, for a certain period of time (cannot remember how long, but it wasn't ages). Then put it in the correct way around.
I tried it, and it worked. It was something witchcraft-y to do with polarisation and negative fields or something like that. There was an explanation about it, but I couldn't understand it.
It worked that's the main thing... I have always found good advice re HRMs and watches on the RW forum/ other runners forums.