What Causes Welts When Pressure Is Applied?

I am getting pressure hives would be the best way to describe them, they are welt like and occur after pressing on my skin for a period time or with great force ex. I fell asleep in my bra and have them around my rib cage, or was carrying and object across my arms and now have a large hive where the weight of the object was resting. also if I bang my elbow or shin on something I get a welt there. they do not often itch unless rubbed or irritated further and are hot like a sunburn, alcohol consumption does not make them occur more but seems to cause the ones I get to worsen quicker and have a longer duration . they started about 3 months ago. around the time I got married and quit taking my birth control pills. I have gone through any and all aspects of my life that may have changed in the time period, ex. detergents, lotions, body washes and shampoo/conditioner, also have expanded list to include foods and drinks. i am not currently taking any supplements or medication other than allegra D which I have taken for the last year and a half for minor season allergies. all of these I have canceled out or quit using to be safe, except for he allegra since it seems to help slightly. the only thing that I can come up with is the birth control, I have been on it for slightly over a decade. is it possible I am allergic to my own new found hormones that may have been quilled by those pills?