There are a couple things that can cause that kind of problem.  Let's deal with size first.  Your toes should fit comfortably in the toe box, with some room to spread out.  Then you should have approximately a thumb-nail width between the longest toe and the front of the shoe.  Lacing too tight could contribute to your problem.  Morton's neuroma might too, but that is usually painful as well. Personally, I don't believe in "breaking in" running shoes.  They should be pretty comfortable from the first wearing.  If not, get something else.  Take a few laps around the store or on the sidewalk outside if they'll let you.  It does sound like a different size might help.

Len

Just thought of this.  Take a few steps barefoot on a hardwood or tile floor and watch how your forefoot spreads as you put weight on it.  Gives you a good idea of how much room is enough to avoid cramping.

Len

Hi Natalie,

I agree with the expert advice of the others and it is a good idea to rotate out shoes anyway in training to avoid placing stress on the same areas over and over again. 

Also, consider your socks and take a look at compression varieties or toe split versions that would add support while increasing circulation and comfort with the correct footwear. 

It is difficult to find the right combination, but the numbness should disappear once you experiment and put together the right pieces. 

Congrats on your first half!