If i'm on an antibiotic for my boil, for 7 days.. can the infection spread to my blood? nothing should get worse since i'm on antibiotic right?

Maybe: With a bacterial infection, an appropriate antibiotic is necessary to fight the infection. Depending on how severe the infection is at the time of the initiation of antibiotic treatment will make a difference if that alone will cure the infection. Decompressing the abcess or lancing it, many times is necessary to effect a more rapid resolution to the problem, if antibiotics alone don't help.