Did you transplant it recently? If you did, it might be going through shock. It probably is also running out of energy for new healthier grow. I went through similar problem with my other berry. I kept them in the platic container from Wal-mart, they had been growing slow and the new leaves were not vibrant. I recently put them in ground, and mix the soil with some "Peat Moss", the new leaves are now looks better, I guess they get more new energy/nutrient now. Raspberry needs acidic soil, get some Peat Moss into your planting area, and get some soil acidifier powder from your local nursery, mix it with water then spray the plant and ground around the plant. It should improve within 2 weeks.

I agree with almost everything rhizo said, but I will add that some natural burlap is treated and should also be completely removed like the synthetic stuff. Also, as stated in rhizo's link, there are conditions where even natural burlap takes much too long to break down. I make it a practice to remove all burlap whenever possible and to remove all that possibly can be removed in situations where 100% of it cannot be reasonably removed (with very large rootballs). The only thing that I don't completely agree with is the need to keep the rootball intact. A lot of the old advice stresses this, but much of the newer information indicates that this is not critical. The important thing is not to leave large air gaps when planting is complete. There are even some (not me) who make it a practice to remove all soil from the rootball before planting, and plant in only native soil. I don't believe that the burlap is playing any part in the problems you are experiencing. The only way it really could is if you had left burlap above ground level and the burlap was wicking moisture from the rootball (a pretty common problem where there is exposed burlap). Except for the wicking issue (which it sounds like you avoided), burlap issues only show up after a few years in the ground.

In other words, it's suffering from nitrogen deficiency. Problem right now is it's too risky to apply chemical fertilizers. Instead add an application of blood meal and some compost. In the fall get those tree spikes for your tree.

Seems like whats happening is they were are low on nutrients, started showing the signs(mainly yellow leaves from not having enough nitrogen) especially now that its blooming it uses more. You noticed and were hoping it was just lacking water and added even more which if anything probably made matters worse by keeping the roots from absorbing what little if any nutrients are left if any from the miracle grow soil. Of course this just speculation and my theory of whats going on, considering Im assuming that they have not been feed besides what nutrients were in the potting soil. If there were the case I would let the soil get back to how you had it and FEED it!!