How to balance training for two events

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I will walk my sixth Breast Cancer 3-day this year and want to run my first Dallas Race for the Cure 5k. The problem is that I work full time plus and the training schedules all have me doing long distances on the weekends. Tomorrow I need to walk 10 miles and run 7 miles and it will be 102 degrees!!!! Any suggestions from experienced athletes? Also, any idea why I can't lose a damned pound?????