my plants dying (no pics)

one of my plants started flowering about 2 weeks ago. It started yellowing and crisping up half way thru veg and its been getting progressively worse. currenty their are 4-5 branches with no leaves on them(some of leaves with burnt tips):confused: . Ive been feeding it all purpose 10-10-10 thru veg and last week i gave it some tomatoe food 18-18-21, no change at all. (im currenty trying to get some nutes for flowering). This is my first grow and i never checked the ph. IMO i believe that ph is too high and i heard when the ph is too high it locks out the nitrogen. so no matter how much i fed it, it was still lacking in nitrogen. am i on the right track? should i leave it the way it is or try to correct it by adding some dolomite?

***the plant was started in the ground around march/april, its about 4' wide and between 10'-15' tall***

At this point the leaves on the bottom should be falling off because they have used up there usefullness, with out a pic can't really tell if thats the case. How often do you feed it, what brand fert., and at what stregnth are you using?, these are all factors. If you over fertilize the same symptoms can occur but worse. miracle grow sux!

i dont feed it much..i been using miracel grow shakin' feed slow release. which feeds up to 3 months(i used that about 2-3 times during veg) and just used this tomato food i bought at k-mart for like 3$:( its water soluble and i used 1 teaspoon for every gallon as directed.

another question..dont sativas double in height during early flowering. i cant complain because the plants already huge but growth has stopped. i was excpecting a 20 footer.