Last year I had a very consistent season with 3 marathons between 3:55 h and 4:00 h and 5 or 6 races between 10k and 10mi with paces between 4:50 and 4:55 / km.
Based off your recent 68 min 10K that you were doing before in 51 minutes and racing only 2 minutes faster (that's not good — you should not be training 2 minutes slower than your racepace)-- you have a very poor aerobic base.