I really feel for you, Coffee, it must be horrible to get your hopes up & then have them crushed. Don't give up hope though, if you are only 10dpo, you might just be testing too early.
Found this about hot tubs. I am guessing the advice would be the same for hot baths.
Men who are trying to become dads should probably avoid frequent dips in the hot tub because the testes are very sensitive to heat. Men's testes are outside the body for a reason — they need to be in a cooler environment to produce healthy sperm.
It can take two to three months to produce a mature sperm cell and it's the immature sperm that are especially vulnerable, so a trip to the hot tub in January can impact developing sperm that's released as late as March, even April.
In the same way, the sperm count of an avid bicyclist who rides nearly every day might be lowered as a result of heat around the scrotum, which is sandwiched between his legs and bike seat.
Hot tubs, bicycling, saunas — even wearing tight underwear — are probably okay in moderation, but a man with a marginal sperm count might want to pass on these activities while he's trying to help his partner conceive.
There's no evidence to suggest that heat affects a woman's eggs, but we do know that hot tubs and saunas aren't recommended during pregnancy. Some studies show that raising your body temperature during early pregnancy increases the risk of birth defects, and a 2003 study found that women who used hot tubs early in pregnancy were twice as likely to miscarry. If you really want to play it safe, skip the hot tub for now or limit visits to the weeks just prior to ovulation.