I have to get my weekly miles up for a marathon but there are just so many 5k's or Halfs I love so much. Can I do a 5k and after I finish run another 15? Also, I have a Half this Saturday, I am hoping to finish and then run 5 more miles is that OK? Or do you just fo the race that day and that's it???
I say do whatever makes you feel the most confident and best prepared. I do not take race days off my regular route unless it is a 10K or beyond. I would not recommend an additional run after the half, but it should be fine following the races of fewer miles.
I only get in trouble on race days when they have beer at the finish line...that always interfers with my extra training plan for the afternoon. In general, I consider the 5k my early workout, but be careful of injury and fatigue. Remember that events are full effort and just avoid pushing yourself to follow a particular schedule of miles on a specific day. I do double duty a lot, but the recovery time has to be extended between outings.
Well, that is my mixed and convoluted answer. See how you feel and evaluate the potential risks/benefits. You are your own best guide.
Running twice a day is not uncommon - but only you know what you're body can tolerate. Like you're considering, I raced a half last fall, and kept on going after the finish line for another 5 to get my miles in for the marathon I was training for. Today I ran a 5K under 19 then ran another 4.5 this evening. A running friend of mine runs 2, 3 5Ks a day sometimes. He's a little nuts, but it's what he likes to do.
A couple things. Running a race at race pace (as opposed to a training pace) is generally considered to be equivalent to a training run about 30% longer, in terms of effort. So the half, if you race it, might be like a 16 or 17 mile training run. If you haven't done this before, be aware that it's hard, probably harder than you imagine. If you decide to do additional miles, do them immediately. Don't give your legs time to cool down and stiffen. Adding miles after a 5K should be easier, though you may have more trouble with pace on the added miles.
I find it easier and better to do my extra miles before the race. Sometimes I will not race the race but run it at MP or the pace work described for the day and then do some miles at the end. I don't think you want to race every week!