That PH is too high. 7 is neutral and most plants like it slightly acidic, so 6.5.

Try working in some compost and some sulphur. If you use mulch try using a pine based mulch as that can also help acidify the soil.

Compost can usually be bought anywhere that sells top soil or garden soil (Lowes, Home Depot, etc) if you do not make your own. Sulphur is usually found with the specialty fertilizers, sometimes called Garden Sulphur.

Reconditioning the soil isn't an instant fix, it might take awhile, but its something you'll need to do.

As for what caused this... certain chemicals or other compounds are high PH, such as cement/mortar/lime.