Am I burning out?

Last week's runs:

Monday: rest
Tuesday: rest (felt blah)
Wednesday: 6x400m at 5:30/km (was supposed to be 9 repeats); 6.44km total
Thursday: 7km easy (very very slow)
Friday: rest (bowling!)
Saturday: 4km easy with Tony :)
Sunday: 18.75km LSD (very very slow, but not at all easy)

Today's LSD just felt wrong. My HR was high (162 average) and my legs felt like lead. They started tightening up after only an hour of running. I stubbornly pushed through and ran for about 2:24, covering less than 19km in that time. Very slow for me, especially when you consider how high my HR was. Ugh. All of my runs felt hard this week. I wonder if I am burning out. I have been going steady since December, when I started building up for the Chilly Half. I have 3 races next month, and was going to start training for the Toronto waterfront marathon at the end of May. Am I really up to training for another marathon? As of right now, my body says no way. I guess I'll have to see how things go over the next month. My racing schedule is:

May 6: Sporting Life 10k (hard tempo run, projected time ~60 min)
May 13: Forest City Half Marathon (going for a PB, goal time 2:05)
May 26: MDS Nordion 10km (going for a PB, goal time 55 min)

I had planned to go all out at the Sporting Life race and take advantage of the downhill course. However, since my relay partner shallonged me to a half marathon duel the following weekend, it would be best not to leave my best performance on the Sporting Life course :P. So, my new plan is to go for a 10k PB in Ottawa. After that...we shall see.